System Description The humidification systems provided with Hanse Environmental, Inc. chambers utilize the latest in ultrasonic nebulization principles to generate the moisture required in the chamber. The ultrasonic nozzle uses air and water under pressure. Atomized water leaving the nozzle is hit by the air reflected by the resonator as sound waves.  It is then nebulized into very small particles, like a fog, and rapidly absorbed by the air. The resonator is adjusted at the factory for maximum atomization and proper fog pattern. The fog pattern can be narrowed by moving the resonator further from the nozzle tip, and conversely, widened by moving the resonator closer to the tip. The water used in the humidification system can be demineralized by the optional  D.I. bottle. In addition, a water quality light is included to monitor the quality of the water generated by the D.I. bottle. The D.I. bottles are a mixture of bed resin that contains positive and negative charged resins.  These resins remove the minerals from the water. The D.I. bottle supplied with the Hanse Chamber is a 1 cubic foot bottle. Installation The nozzle(s) is installed at the factory for proper distribution of the moisture introduced into the chamber. Even though the nozzle(s) is designed for the temperature extremes experienced in the normal operation of the chamber, it is recommended that the nozzle(s) be removed when humidification testing is not being performed. The nozzle(s) mounting brackets are designed for ease of installation and removal. The direction of the nozzle(s) has been determined at the factory to maximize the distribution of the moisture within the chamber and should be maintained within the configuration. The nozzle(s) is  provided with hose connections that can be made within the confines of the chamber when installing or removing it. This will reduce the time required to go into humidification testing. Operation The water and air supply to the nozzle(s) is regulated by in-line pressure regulators. The water pressure to the nozzle(s) is adjusted at the factory to provide the proper amount of moisture to the chamber. The air regulator should be adjusted to maintain the air pressure to the nozzle(s) at a  minimum of 15 psi above the water line pressure. This is necessary to provide enough air pressure to open the water valve internally to the nozzle. This will  allow atomization to begin. The air and water supplies to the nozzle(s) are controlled by 24 vdc control valves. The valves are controlled by the mode of operation of the chamber. When the humidification mode is disabled, Event 4 (digital out 4), the water supply is turned off ,and the line(s) is vented to drain. Similarly, the air lines are turned off and ported to exhaust also. This prevents an inadvertent operation of the system. When humidity is called for, Event 4 (digital out 4) enabled, and the nozzle(s) have been installed in the chamber, the water valve opens applying pressure to the nozzle(s). In addition, when the set point is above the humidity level in the chamber, the air valve opens which applies air pressure to the nozzle(s). This air pressure results in the opening of the water valve internal to the nozzle(s) and the atomization process is started. As the humidity level in the chamber reaches the set point, the control system will start controlling the air valve to take control of the humidity level in the chamber. The valve will remove air pressure from the nozzle(s) for longer and longer periods to control the humidity level within the set point parameters. If the humidity function is turned off, Event 4 (digital out 4), then the system reverts back to the condition described above and the air and water lines are ported to exhaust condition. At this point the nozzle(s) can be safely removed from the chamber once they have cooled off. If during normal operation of the humidification system the water quality light goes from green to red, the D.I. bottle should be scheduled for regeneration at the earliest possible time with out interrupting a test. The water quality light may indicate red if the system has been sitting for some time between operation. To test if the water is OK, run a small amount of water through the system. The light will turn green immediately if the D.I. bottle is OK. If the system is going to be operated for long periods of time in the humidification mode, it is recommended that a second D.I. bottle be installed with the water quality light in the line between the bottles. In this matter, if the light indicates that the water quality from the first bottle is not in spec, the water is still being treated by the second bottle and will continue to meet the water quality requirements of the system. When the humidification test is completed, put a second bottle in the place of the first bottle, have the first bottle regenerated and place it no the location of the second bottle. In this matter you will utilize the bottles to their maximum, and not regenerate them unnecessarily. Maintenance The humidification nozzle(s) do not require routine maintenance. The water supplied to them should be free of debris and suspended solids, and it is recommended that a 10 micron filter be installed between the chamber and the water supply. This will prevent premature plugging of the nozzle tip. The D.I. water bottles will require periodic regeneration that is dependent on the frequency of use and the quality of the raw water system. If the chamber is to be installed in a location that has particularly hard water or water with high mineral content, it is recommended that a second D.I. bottle be installed, or a small Reverse Osmosis system be installed ahead of the D.I. bottle(s) to extend their life. This system can be sized by the factory and local installation arranged if desired. Regeneration of the D.I. bottles can be done by any qualified pure water vendor. In Michigan, call Hi-Tech Environments at (810) 620-3333 for the name of the nearest qualified vendor or to arrange for replacement bottles.

Overview HanseView allow for remote control through text files. This can be done on a local computer or via file sharing. Basic concept is that a command written to a text file is read by HanseView then executed and output placed to a text file. This remote control capability allows for test stand integration. You can then use 1 of two models. Have test stand send set point commands or profile start stop commands to control chamber then read back current status. Other option is to have test stand read only status and react to conditions and time to perform necessary equipment test. Video Tutorial Simple Demonstration Note on Version 3 HanseView program directory is been moved out of Program directoy and placed by default C:\HanseView instead of C:\Program Files\HanseView. Run: Notepad Open: "C:\Program Files\HanseVIEW\Chamber.INI" Find Section: "[System Parameters]" Add or Change:Remote Control File=C:\Program Files\HanseVIEW\RemoteControl.txt Save & Close file Run: HanseVIEW Run: NotePad Open: "C:\Program Files\HanseVIEW\RemoteControl.txt" Type: run Save the File Hanseview will start with stop code "Remote Start" Defining Remote Control File C:\Program Files\HanseVIEW\Chamber.INI contains section [System Parameters]Remote Control File=C:\Program Files\HanseVIEW\RemoteControl.txt This specifies the file you will write to. HanseVIEW will only load new setting on startup For Status see included "RemoteControl.txt" file and "RemoteControl.status" response file HanseVIEW tracks changes to the file and executes ASCII text commands written to the text file. Basic Commands Run Start the currently loaded profile to run stop Stops currently executing test status Writes current time/date and test status to RemoteControl.Status file (text file) load c:\Program Files\HanseVIEW\Profiles\Default.vcm Loads profile Default.vcm into the controller Added manual controls to file interface in 2.2.3 mant sp,rate Manual set point and rate for temperature manv sp,rate Manual set point and rate for vibration mana hex Manual auxiliaries see table bellow. This is a conversion of 16 bit binary to hex. First bit is Aux 16 last bit is Aux 1 Sample Programs: Sample BASIC Program to run chamber fileno=FreeFile() Open "c:\Program Files\HanseVIEW\RemoteControl.txt" for output as fileno Open "c:\Program Files\HanseVIEW\RemoteControl.txt" for output as fileno Open "c:\Program Files\HanseVIEW\RemoteControl.txt" for output as fileno Print#fileno,"run" Close fileno Sample BASIC Program to stop chamber fileno=FreeFile() Print#fileno,"stop" Close fileno Sample BASIC Program to load a profile fileno=FreeFile() Print#fileno,"load c:\Program Files\HanseVIEW\Profiles\Default.vcm" Close fileno Notes These samples assume both programs are running on same computer. UNC network name can be substituted for "c:\Program Files\ChamberView\" to run remotely. Appropriate error handling ust be added for unavailable files or machines. Actual "RemoteControl.txt" file spec is defined in HanseVIEW setup, but it should be local to HanseVIEW controller due to poll rates. We generally put the Remote Control file in a directory by itself with read/write privileges if network access is desired. Response file is always C:\Program Files\HanseVIEW\RemoteControl.status If network access is desired this directory is shared with Read/Only Attributes. Status File Format If you install the demo & HanseVIEW software on same computer this should also work for you. If you ran HansVIEW PRIOR to running the demo the first time, you would need to restart HanseVIEW to activate the remote control. Example Status File. Please note yours will change based on what options and inputs are selected. It is bes to make your prgram search the Varaible name to find it's value May 29, 2014 14:34:29 Channel 3 Temp Below Low Limit Data directory C:\HanseVIEW\Data\AAR\Thermal Test Out\Heat Step Test Out Elapsed Time 0:00:06 Remaining Time 1:55:3600 Profile Segment 1 Vibration1 Process Variable  0.000000 Vibration2 Process Variable  0.000000 Vibration3 Process Variable  0.000000 Vibration4 Process Variable  0.000000 Vibration Controller Process Variable 0.000000 Vibration SetPoint -299.899994 Product Process Variable 25.000000 Air Process Variable 25.000000 Temperature Setpoint -299.899994 Temperature3 Process Variable  -56094.765625 Temperature4 Process Variable  -56094.765625 Temperature5 Process Variable  -56135.703125 Temperature6 Process Variable  -56135.703125 Temperature7 Process Variable  -56135.703125 Temperature8 Process Variable  -56094.765625 Temperature9 Process Variable  -56094.765625 Temperature10 Process Variable  -56135.703125 Temperature11 Process Variable  -56135.703125 Temperature12 Process Variable  -56135.703125 Temperature13 Process Variable  -56133.664063 Temperature14 Process Variable  -56133.664063 Temperature15 Process Variable  -56133.664063 Temperature16 Process Variable

There are always beginners in any field.  The economic conditions over the past year or so have changed the business climate.  Many are opting to take early retirement if offered.  Because of massive layoffs, people are being asked to do work that they have never done before.  Mergers may mean that you suddenly own equipment that you don’t know how to use.  And there will always be people new to a field out of their own choice – perhaps fresh out of college or transferring from another department.   Working with HALT is an exciting challenge.  I’ve been deeply involved with the process for over a decade now.  I meet a lot of engineers that have a very good understanding of the process, but have lately been seeing that there are a lot of people who don’t know very much about it and would like to learn more.  There is also a crowd who would rather debate semantics that get down to work.   Let me start by saying that there is no one right way to run HALT.  Let’s take a minute to review what HALT is, and what HALT isn’t. Usefulness of Accelerated Testing   No matter how you look at it, business is tough right now.  Customers are expecting more for less, whether that customer is a personal consumer, a government agency, or another department within your own business.  People want high reliability, low cost, the latest technology, and something that will last.   Let’s face it; it’s difficult to please everyone.  You need to beat your competitor to market, but make sure that your product is going to last.  How do you go about doing this?   One of the easiest ways of taking care of most of these issues is by accelerating the testing process.  You can’t afford a 20 year test to see if a light bulb is going to last 20 years in your neighbor’s kitchen.  You need to speed things up.   You can make the light bulb fail simply by pushing it off a table.  It doesn’t teach you much, though, other than that gravity still works.  What is needed is a logical approach that allows you to “accelerate” the time, making the working environment like a time machine that can show you what failures are bound to happen.  There are computer programs and different scientific formulas that can help you to make a correlation against possible lifetime, but the main point is that you will see what failures are most likely to happen out in the field.  You should be able to find out within a matter of days what you might not have been able to find out for years.   Why is this important?  One major company expense is warranty issues.  Every time that Ford Motor Company finds a failure and fixes the weakness before the part can get into a car out on the road, their accounting department comes back and tells them how much Engineering just saved their company.  You can literally save yourself millions by catching something early.  This also adds to customer assurance.  You win by saving money, but also make more money by getting repeat business.   Starting Temperature The best way to start the test is at laboratory ambient.  Why, you may wonder, do I use that term?  I am a member of several working groups for the IEC (International Electrotechnical Commission).  We have found that the term ambient, over the years has come to mean different things to different people.  In the older definition of ambient, it is the chamber temperature around the product at any given time.  However, most people use it as the room temperature that they are doing their testing in.  By using the phrase, “laboratory ambient”, I am trying to make sure that people understand to start their testing at about room temperature.  I don’t want anyone to be confused with whatever temperature the last test in the chamber left off at.  Better safe than sorry!   Remember to constantly monitor the product. Ford Electronics, before becoming Visteon, reported publicly that 50% of failures of intermittent and would not have been caught without constant monitoring.  It’s not good enough just to take a reading at the beginning and a reading at the end.   A Series of Tests Keeping in mind the thought that there is no one perfect way to run a HALT, here are a few basic thoughts that should be kept in mind.  HALT is actually a series of tests.  You should have more than one unit available for the testing, preferably one for each test of the series.   From the purist standpoint, the best way to start is by testing using single environments, then run with combined environments for comparison.  These are the six standard tests that we recommend, though this could be done in other ways:   Cold only Heat only Vibration only Heat with vibration Temperature swings Temperature swings with vibration   Others, of course, can be added.  If you are concerned about lower temperatures, you may want to add Cold with vibration.  If you are worried about humidity, you should do a humidity only test and then start combining it with other environments such as thermal and vibration.  Power cycling can also be very beneficial.     Before the tests even start, you should be thoroughly familiar with the product to be tested.  You should know as much as possible of the end environment that it will be placed in, then test accordingly.  Remember:  End users are always harder on a product than you will expect them to be, and they will expect it to continue working anyway.   Step by Step Once you’ve decided which environment, how do you start?  They key is knowing your product.  Is it as small as a PCB?  Is it as big as a tank?  How long will it take to stabilize at a temperature?  Are some components more likely to fail than others?   Along these lines, how do you know if your product is stabilized at temperature?  Let’s use the example of what I will be testing today.  It is a console for a vehicle that is roughly the same width as the ceiling of the van.  There is no way that you could choose one representative spot on it and feel that the entire unit will be the same.  The simple rule of thumb is:  the larger the product, or the more diverse components it has, the more thermocouples need to be used.   You will still control off of one main thermocouple.  This should be placed where it is either representative of the entire unit or on the most sensitive component, depending upon your main concern.   A good starting place for all of the tests is to start at laboratory ambient.  This is typically somewhere around 25°C.  Fixture your product, if necessary, and hook up any wiring that may need to be in place.  Keep in mind that your wiring or cabling will be seeing the same extremes as your product!   The order of the tests is completely up to you.  However, keep in mind that if you start with single environments, and then move to combinations, you will get a good baseline for what you can expect.  For example:  if your first test is heat combined with vibration, and you find a failure, can you tell by looking at the product which caused the failure?  Or was it a combination?  If you have already run a heat step test and a vibration only test, you can more readily see which of the environments caused the failure or if it was the combination of environments.   What is a Failure? Different companies will judge failures differently.  I went to one company where they had product set aside because of pinpoint scratches in the paint job.  To them, that was considered enough of a “failure” in the product that they refused to ship it out to a customer.     To some, the first intermittent failure is as far as they want to go.  Others will want to get all of the way to a hard failure.  This is something that you should keep in mind when you are planning your test – what will you consider as a failure?   The Tests Now that we’ve reviewed the main points that you need to think about before the test, let’s take a look at the tests themselves.  It’s important to know that there is more to it than just pushing the “Run” button on the computer.  You’ve already seen that you have to think things through in advance.  We’ll take a look at the different considerations for each of the tests, and the reasons for running them.   Cold Step Test Using cold temperatures tends to be the least destructive of all of the single environments.  That makes it a good starting point for doing testing.   You can choose the size of the steps based upon your knowledge of the product.  If, for instance, you are concerned about the effects of cold on it, you should make the steps smaller.  If you are looking for baseline data, you may want to start with larger steps, then make them smaller if you have a premature failure.  With cold, many engineers are comfortable starting with steps of 10°C per minute change rate.   Once you’ve decided on your ramp rate, you need to decide your dwell time.  How long should your product stay at temperature before ramping again?  The prevailing opinion is that you keep the dwell time to the minimum needed to stabilize the product.  For something like a PCB, this may be only five minutes.  If you are testing an assembly it may need to be longer.  Again, you need to use your own expertise to decide.     Take a look at the following graph: The chart above shows an example of what could be used.  Starting at laboratory ambient and holding until stabilization, the test lowers 10°C as quickly as possible, and then holds for ten minutes.  These steps are continued until there is a failure. Heat Step Test The heat test is very similar, just going the other direction.  It is based on the same principles as the cold step test.  First, settle in at laboratory ambient, then begin ramping and dwelling.  Heat tends to be more destructive than cold, so you may choose to raise your temperature only 5°C per minute instead of going faster.     I had the chance to work with a company once whose product was going to end up in a hospital environment.  Their first hard failure came at only 2°C above laboratory ambient.  At first they weren’t concerned, reasoning that hospitals are air conditioned and so they should never have to worry about the surrounding air getting too warm.  I let them know of an extended hospital stay that I had where the temperature was controlled based on time of year, and the heating automatically kicked in because of the date, not because it was needed.  Patient rooms ended up at close to 30°C.  The customer reworked the board, and their unit is now number one in the market.  Moral:   Make sure that you have a gap between expected use circumstances and what your product can actually survive through.  Set it up in your mind as a worst case scenario, and then add a percentage.  To paraphrase, if it can go wrong – it will go wrong.   Vibration Only Test You’ve gotten through the easy tests, heat and cold.  You’ve monitored and data-logged.  You’ve made any changes that you feel are necessary.  Now you are ready for vibration. Once again you will start with the temperature at laboratory ambient.  We do this to make sure that temperature is not going to affect the test. It may not seem like a real world situation, but right now we are concentrating purely on the vibration.   The standard way of measuring a vibration test is through the g level.  Here a g, there a g – where do we measure the g from?   If you measure from the bottom of the vibration table, what you are really reading is what the table is doing.  This may have very little to do with what your product is doing.  The best placement for the accelerometer is on or near your product.  Some prefer to attach the accelerometer to the fixture holding the product in place.  This is perfectly acceptable.  If there is no easy way to affix it to the product or fixture, then you should mount it near the fixture on the table top.  This will give at least a close approximation of what the product is seeing.   Vibration, as opposed to temperature, needs to be handled in very small increments.  It can be difficult to control very tightly, so we suggest starting a 2 g’s and moving up 2 g’s at a time.  The dwell time, again, is up to you and your knowledge of your product.  There should be an ample settling time, so ten minutes is often used.  You continue stepping up until you see what you consider to be a failure, again monitoring and data logging as you go. Combinations Now comes the fun part.  You’ve gotten done with the boring steps.  You’ve already learned more about your product, and about the responses of your other team members.  (“You’re doing what to my design?”) Thermal Swing Test You’ve already done cold, heat, and vibration.  The next logical test is thermal swings, combining the heat test with the cold test. Set the chamber to begin at laboratory ambient and allow the product to settle in.  Decide whether you would rather go hotter or colder first.  Adding nitrogen to the chamber air will help to get rid of any latent humidity in the product, so this should be part of the consideration.   Decide on the amount of the ramp, typically either 5 or 10°C at a time, and decide upon your dwell time.  Then get started.   As you can see by the chart, each step gets wider.  Say that you choose to ramp with 5°C increments and your starting temperature is 25°C.  You’ve chosen 5 minute dwells and think that you would like to go hot first.  Here is the basic scenario: Continue testing until failure.   Note:  It is not unusual for a product to fail at extremely low temperatures, then come back to working order once more when warmed up.  If you find a failure during the cold portion of this test, it is advisable to go on to the next hot step and find out if it starts working again.   There are valid reasons for doing the swing test.  The difference between thermal coefficients is what can cause parts to pull away from each other, sometimes causing cracks.  By applying these changes as fast as possible, we are stressing the unit beyond what it would normally see.  There are people that claim that you will never see a temperature change of over 30°C per minute in most circumstances, but consider the following:   I live in Michigan.  We are not the coldest winter state, but it is very typical to get a wind chill of -40°C at least once every winter.  Say that my car gets stuck in the snow within a mile or so of home.  I decide to walk (we Michiganders are a hearty breed).     My cell phone just went from around 25°C to -40° as I stick it to my ear to call my husband and tell him of my poor luck.  Since he is out on the road, I have to pull out my trusty palm computing device to get his number.   I get home, shivering, turn the heat up and stand over the heater – still using my trusty phone.  The phone and computer warm back up to 25°C with the hot air rushing against them.  By this point, not only have the electronics been stressed but so have I!  I’m sure that you can think of other severe circumstances that we tend to put electronics products through. Heat with Vibration Test Let’s do some shake and bake.  Not dinner – although it’s been done!  It’s time to use heat and vibration together to test your product out.   What do you choose for your vibration level?  Let’s say that you know that your product showed a failure at 10 g’s in the previous vibration only test.  Since you already know that this is the breaking point, you don’t need to go right up to that.  You are trying to learn what will happen when you combine thermal factors with the vibration.   Most of the engineers that I have worked with choose a level that is about 80% of the breaking point.  In this case that would mean 8 g’s. What’s the best way to do a combined heat and vibration test?  Now you get to rely on your expertise once again.  It is best to follow closely to the original heat test that you did, once again starting at laboratory ambient.  That will give you a guide as to where you would expect your product to show a heat related failure.  If the temperature was extremely high, you may want to skip some of the lower temperatures.  Say that your product didn’t show a failure until 110°C – you may want to settle in at 60° or so and start your steps from there.   The example in the above chart shows ten minute dwells, with vibration being run (lower than failure level) for two minutes out of every 5.  Pulsing can cause failures, but so can constant running.  It is up to you to decide the best way to run the test.   This is where comparison gets interesting.  The typical result will be that the product will fail at a slightly lower temperature once vibration is added than it will using heat alone.  There are always exceptions to every rule.  This particular test should tell you a lot about how your product will survive a combination, which is what it will no doubt see in real life usage. Thermal Swings with Vibration Test Using the data that you learned from your heat plus vibration test, apply the same principles to your thermal swings plus vibration.  Again, you may want to skip ahead a number of steps if your failure was quite a ways from laboratory ambient.   I learned something very interesting from a machine design magazine article.  Some companies are using extremely cold temperatures to “de-stress” equipment that will go into a high vibration area.  Typically we learn that anything that we do to a product will end up taking life out of it.  After applying the principles found in this article, I ran a few experiments with customers with totally different types of products.  In each case, by combining vibration with cold temperatures, we found that they could actually withstand more vibration than they could at ambient.  You may find this same result while you are doing your swing test with vibration.  You may also want to add a cold test with vibration if your product is bound to have to survive low temperatures. Now What? You’ve got all of these numbers and failure times.  Now what do you do?  What do you want to do?   There’s no reason to build a brick outhouse.  (This is a family magazine – I’m sure that you’re familiar with the more common phraseology.)  If your product has lived up to what it needs for real life, plus a reasonable margin, you may not want to do anything to change it.  Microsoft, for instance, after doing testing found that they could extend their warranty from one year to three on their mouse and still not worry about warranty issues.   If you don’t end up breaking something, that doesn’t mean that the failure is in you.  It most likely means that you have an extremely tough product ready for market.  If you do find a failure, think of it as a good thing.  HALT is a learning tool.  You are looking for a premature end of life to your product.  It allows you to learn something quickly that might have taken months, and a lot of warranty replacements, to learn otherwise. No Magic Bullet If you do a HALT test, will you somehow be able to tell exactly how long the life of the product will be when put out on the market?  Probably not.  Unless you already have field failures on the same product, or one almost identical, it can be very hard to make a true time correlation.  If you have field failures and can reproduce them in the lab under certain stresses and a given amount of time, the answer is yes.  In that case you can make a good correlation.   Is a rapid thermal cycling chamber with tri-axial vibration the only chamber I will ever need again?  If that was so, I’d be a millionaire.  I have a hammer, screwdriver and wrench in my toolbox.  I can’t choose just one tool and feel that I can fix everything.  The same goes for test equipment.  HALT is an extremely valuable tool, but should not be considered your only one.   One of the best industry changes that I’ve seen is willingness for engineers to start sharing more non-proprietary information.  If you want to learn more about HALT, look into groups like the IEEE AST (Advanced Stress Testing) group, take a seminar, and look into user groups.  It is wonderful that people are starting to share more information so that we don’t all have to start at square 1.  Look to people that you know you can trust. Final Note The most important thing to remember when you are doing HALT testing is to rely upon your own knowledge of the product.  Preplan, knowing the end use environment.  If you have plastics, know your melting points.  Keep an open mind as you test, remembering that a product failure is not the same as a personal failure.  Work with design engineers, project engineers, production engineers, management, and anyone else who can give good input.   I love working with HALT.  There is no other industry that I would rather be in.  I feel like the people at BASF – “We don’t make the _____ … we make it better”.  I get the chance to help people make a better product.  That leads to higher reliability, lower costs, more safety and security.  As a child I wanted to help bring peace to the world.  As an adult I found that it is hard to make such widespread changes.  Now, as a teacher and manufacturer, I find that each one of us can make a difference and help the world to be a little bit better place to live in.  You now have the possibility of doing your job better than ever before, turning out a better product for less money, and making someone else’s life a little bit safer, easier, less expensive, and more reliable.

Ford Motor Company has been using Hanse Environmental testing systems for years. See the video below by Ford on the use of our testing systems.

A Tutorial by Lloyd W. Condra, Hanse Environmental, Inc. Environmental stress screening (ESS) is one of the most widely used of all accelerated reliability tests. It precipitates latent defects, which are detectable only with the application of stress. Latent defects are introduced into the product during manufacturing, since design-related defects should have been detected and eliminated by reliability-enhancement testing during the design phase. Figure 1 illustrates the ESS concept. ESS is effective only for a product with an infant-mortality region, which is indicated by a decreasing initial failure rate in Figure 1. The optimum ESS time is t0, since at that point, all the infant-mortality defects have been screened out. If ESS ends before t0, the product still contains infant-mortality defects which will be found by the user of the product. If ESS ends after t0, useful life is consumed without improving the failure rate. The failure rate may not be zero even after t0. The failures occurring after t0 are not infant-mortality failures though, and they must be dealt with in ways other than ESS. Many attempts have been made to prescribe standard ESS processes, but since ESS processes are product-specific, the most effective ones are based on a knowledge of the product, its potential defects and the stresses that cause them.1,2,3,4 An effective ESS process generates valuable data which can be used to improve the product as well as to screen out defects. Unfortunately, when ESS is viewed only as a requirement imposed by the customer or the market, its full benefits are not realized. The compliance-based approach treats ESS like a cookbook process, in which the product is exposed to a standard set of stresses, at standard levels, for standard lengths of time. Little attention is given to the failure mechanisms, to how they are distributed in time, or to how the failure data can be used to improve the product. Compliance-based ESS provides few benefits other than satisfying a customer-imposed requirement. Compliance-based ESS users can incur unnecessary expense. Table 1, 2 shows a typical ESS program implemented by a manufacturer of aerospace electronics equipment. From a physics-of-failure point of view, these conditions are practically identical and, with minor modification, they could all be conducted in a single environmental test chamber. Since the compliance-based approach does not bring this level of understanding to the process, each condition was implemented as stated, and a separate test chamber was required for each one. The physics-of-failure approach to ESS is based on an understanding of the potential types of latent defects in the product, the failure mechanisms and the stresses that cause them.5,6,7 The ESS conditions are set up to precipitate those defects, and the data is used to determine their causes and distributions. Failure data is communicated to the appropriate design and manufacturing personnel and used to make changes to improve the product. If it is properly set up and operated, a physics-of-failure ESS process can be extremely cost-effective. Setting Up the ESS Process ESS is product unique, since each product has its own set of potential defects and since the applied ESS stresses affect each product differently. Even though the ESS process must be set up individually for each product, there are many common features of both products and stresses which cause many ESS processes to be similar. The stresses applied in ESS are expected to precipitate manufacturing defects. They are not necessarily those the product will see in service. The two most common ESS stresses for electronic products are temperature cycling and vibration. They may be applied sequentially or simultaneously. It is critical that electronic equipment be monitored during ESS. This is the only way to detect failures under extreme conditions. More importantly, the stresses used in ESS can induce reversible damage not detected in tests conducted at ambient conditions. This induced damage is itself a latent defect, and the ESS process can actually cause early field failures. Reducing or Eliminating ESS Since ESS is an inspection step, it does not add value to the product and should be reduced or eliminated as quickly as possible. This cannot be done without proper justification, which requires relevant data. ESS must be set up to provide data which can be used to reduce or eliminate it. The following eight steps illustrate what should be done: 1. Collect failure rate data during the ESS process. Failure data must be collected, not just at the beginning and the end, but during the ESS process. It is not enough to know that failures occurred; their time of occurrence must be recorded. Data from all ESS attempts, whether or not there was a failure, must be collected and recorded. 2. Prepare a plot of failure rate vs time. This is the type of plot shown in Figure 1. If the failure rate decreases with time, there is an opportunity to reduce it if proper product improvements can be made. If the curve is constant, or if it increases with time, the ESS process cannot be effective because either there are no infant-mortality defects or the wrong stresses, or levels thereof, are being used. If this is the case, ESS should be modified or discontinued and some other means of product improvement must be implemented. ESS may be conducted anywhere in the manufacturing process flow. Table 2 shows some examples of the types of stresses used for ESS at the component, subassembly, assembly and system levels for electronic equipment.8 Table 38 shows the types of defects which may be detected by temperature cycling and vibration. The specific levels of ESS stresses are selected to precipitate the relevant defects in a relatively short time, and yet not consume a significant portion of the life of non-defective items. For electronic equipment, the lower end of the temperature cycling range is usually from -40(degree)C to -50(degree)C, and the upper end is from +75(degree)C to +85(degree)C. The rate of temperature change can also be important. Figure 2 illustrates the effects of temperature rate-of-change on surface-mount transistor lifting.7 Selecting the vibration level can be quite challenging, especially if the defects are susceptible to a range of frequencies. In general, multiaxis, repetitive shock vibration is much more effective and efficient than single-axis vibration. Simultaneous temperature cycling and vibration also are much more efficient than either separate or sequential application of the two stresses. 3. Analyze failures and separate them according to failure mechanism. All failures must be analyzed in order to take corrective action. It is truly amazing that many ESS operations do not include any structured method to analyze the failures and to provide the results to those who can take the proper corrective action. 4. Prepare plots of failure rate vs time for each failure mechanism. After this is done, the criteria of Step 2 must be applied to each failure mechanism. Again, only failure mechanisms with decreasing failure rates can be attacked with ESS. 5. Improve the product. Without using the data generated by ESS to improve the product, including design, components, materials and processes, there is no hope of reducing or eliminating the ESS process. If the staff responsible for the ESS process is not the staff responsible for designing and manufacturing the product, it is important that good communication take place between the two groups. 6. Collect and analyze ESS data for the improved product. If the proper steps have been taken to improve the product, then the area under the infant-mortality region of the failure rate vs time curve should be smaller. This may result from either a reduced slope of the curve or from a shorter time in which it reaches a constant failure rate. 7. Modify ESS conditions to reflect the new failure rates. As failure mechanisms are eliminated, the stresses that precipitate them may be eliminated. If they occur in shorter times, then the duration of the ESS process may be shortened. In some cases, additional stresses or increased levels may have to be introduced to detect failure mechanisms which were not expected. If this is the case, care must be taken to avoid introducing irrelevant failures. 8. Reduce or eliminate ESS as warranted. If the ESS process has been set up properly, and if the proper data is collected and used effectively, it will result in a continuously improving product. Eventually, a point will be reached where the ESS process may be reduced significantly or eliminated entirely. It may also be possible to reduce the frequency of ESS by going from a 100% screen to a sample screen. The effectiveness of ESS ultimately must be evaluated economically. This analysis is based on the cost to conduct ESS, the cost of field failures, and the frequency of occurrence of field failures.7,9,10,11,12,13,14 ESS costs include the cost of capital equipment, the recurring cost of conducting the process, the cost of analyzing and repairing failures, and the risk of actually introducing new failures into the product. The benefit is in the reduced costs of field failures. Effectiveness of ESS The references contain many examples of the successful use of ESS. AT&T called its process environmental stress testing (EST) to emphasize the fact that the company used the results to make product improvements.15 The process combined temperature step stress and temperature cycling between -20(degree)C and +70(degree)C for circuit card assemblies. Figure 3 shows a plot of failures vs the number of cycles in the EST process. From the data in Figure 3, the investigators concluded that the optimum number of temperature cycles was 16. In addition to the improvement in outgoing quality, the investigators tracked field failure results. They reported a five-fold improvement in product which had been exposed to EST, compared to product which was not exposed to EST. Although some ESS practitioners believe that the process should always be conducted on 100% of the product, a sample EST process has been implemented successfully.15 One two-stage ESS process for laser diodes was comprised of a steady-state burn-in at 165(degree)C and 10 kA/cm216 The results showed that unscreened lasers had a medium lifetime of about 600 h, compared to about 6,000 h for screened lasers. for 2 h prior to assembly, and a second steady-state burn-in at 70(degree)C for 150 h after assembly. In another study on laser diodes, AlGaAs laser diodes were exposed to an ESS process consisting of operation under power in inert atmospheres.17 The results are shown in Table 5. Again, significant improvement in operating reliability was obtained for products which had been exposed to ESS. If a product has a very low failure rate, the design and operation of the ESS process can be quite complex. McClean reported the use of a technique called highly accelerated stress audit to screen printed-circuit card assemblies.18 The screening stresses were temperature cycling and vibration, with power being applied during the process. As the name implies, the test was applied on a sample basis. As noted in these examples, the development and operation of an ESS process must be highly customized to the product being screened. Perhaps the greatest benefit of ESS is the hands-on knowledge and experience about the product gained by those who design and manufacture it. For this reason, it is not a good idea to assign the ESS process to a reliability department or a third-party screening organization with limited capability to change the design or manufacturing processes. Alternatives to ESS ESS is effective only when the product has an infant-mortality region. If this is not the case, other methods must be used. Some other methods which also involve the application of stresses are ongoing reliability testing (ORT), ongoing accelerated life testing and periodic requalification. ORT exposes a small sample, for example, less than 1% of production on a regular basis, to stresses at or slightly above the operating range for periods ranging from a few days to a few weeks. All failures are analyzed, and the data is used to improve the product. At the conclusion of the test, the surviving samples are shipped as regular product. Ongoing accelerated life testing is similar to ORT, except that the stresses are somewhat higher, and the test is continued until the samples fail. Since this is a destructive test, the sample sizes may be somewhat smaller than those of ORT, especially if the product is an expensive one. Periodic requalification involves the repetition of the qualification procedure, or an abbreviated version of it, on a periodic basis (usually once or twice per year). This type of test had its beginning in some of the U.S. military standards. Since periodic requalification does not involve a wide range of sample lots and since it is expensive, it is losing popularity. Summary The overall purpose of ESS is to assure that, once a product is qualified, there will be no uncontrolled variations in the individual items during the production phase. The application of stresses is necessary to detect some defects which cannot be observed by functional or visual observation. The only realistic way to develop and operate an effective ESS process is to use the physics-of-failure approach. This requires an understanding of the product, and knowledge of the types of defects and the types of stresses which precipitate them. Almost by definition, a significant amount of trial and error is associated with developing efficient ESS processes; but once the basic knowledge is gained, it can be applied to a wide range of products. In most cases where ESS has been implemented, it has proven to be quite effective in reducing overall product costs. References 1. MIL-STD-2164 (EC), Military Standard Environmental Stress Screening Process for Electronic Equipment. 2. DoD-HDBK-344 (USAF), Environmental Stress Screening of Electronic Equipment. 3. Environmental Stress Screening Guide, Technical Report No. AD-A206, U.S. Army, Ft. Belvoir, VA, January 1989. 4. Environmental Stress Screening Guidelines for Assemblies, Institute of Environmental Sciences, March 1990. 5. Pecht, M., and Lall, P., "A Physics of Failure Approach to Burn-In," Proceedings of the ASME Winter Annual Meeting, 1993. 6. Lambert, R.G., "Case Histories of Selection Criteria for Random Vibration Screening," The Journal of Environmental Sciences, January-February 1985, pp. 19-24. 7. Smithson, S.A., "Effectiveness and Economics--Yardsticks for ESS Decision," Proceedings of the Institute for Environmental Sciences, 1990. 8. Mandel, C.E.N., Jr., "Environmental Stress Screening," Electronic Materials Handbook, Vol. 1, ASM International, Materials Park, OH, 1989, pp. 875-876. 9. Smith, W.B., and Khory, N., "Does the Burn-In of Integrated Circuits Continue to be a Meaningful Course to Pursue?," Proceedings of the 38th Electronic Components Conference, IEEE, 1988, pp. 507-510. 10. Pantic, D., "Benefits of Integrated-Circuit Burn-In to Obtain High Reliability Parts," IEEE Transactions on Reliability, Vol. R-35, No. 1, 1986, pp. 3-6. 11. Shaw, M., "Recognizing the Optimum Burn-In Period," Quality and Reliability Engineering International, Vol. 3, 1987, pp. 259-263. 12. Huston, H.H., Wood, M.H., and DePalma, V.M., "Burn-In Effectiveness - Theory and Measurement," Proceedings of the International Reliability Physics Symposium, IEEE, 1991, pp. 271-276. 13. Suydo, A., and Sy, S., "Development of a Burn-In Time-Reduction Algorithm Using the Principles of Acceleration Factors," Proceedings of the International Reliability Physics Symposium, IEEE, 1991, pp. 264-270. 14. Trindade, D.C., "Can Burn-In Screen Wearout Mechanisms?: Reliability Modeling of Defective Subpopulations--A Case Study," Proceedings of the International Reliability Physics Symposium,IEEE, 1991, pp. 260-263. 15. Parker, P.T., and Harrison, G.L., "Quality Improvement Using Environmental Stress Screening,"AT&T Technical Journal, July-August, 1992, pp. 10-23. 16. Chik, K.D., and Devenyi, T.F., "The Effects of Screening on the Reliability of AlGaAs/GaAs Semiconductor Lasers," IEEE Transactions on Electron Devices, Vol. 35, No. 7, July 1988, pp. 966-969. 17. Tang, W.C., Altendorf, E.H., Rosen, H.J., Web, D.J., and Vettiger, P., "Lifetime Extension of Uncoated AlGaAs Single Quantum Well Lasers by High-Power Burn-In in Inert Atmospheres,"Electronics Letters, Vol. 30, No. 2, January 20, 1994, pp. 143-145. 18. McClean, H., "Highly Accelerated Stressing of Products With Very Low Failure Rates,"Proceedings of the Institute of Environmental Sciences, 1992. About the Author Lloyd Condra wrote this article while employed as a consultant to Hanse Environmental, Inc. Today, he is a Principal Engineer at Boeing Company in Seattle. Previously, he was affiliated with AT&T Bell Labs, Medtronics and Eldec. Mr. Condra is a graduate of Leigh University with an M.S. degree in material engineering, and is the author of two technical reference books. Hanse Environmental, Inc., 235 Hubbard St., Allegan, MI 49010, (269) 673 8638.

Since the early 1980's there has been much discussion regarding various approaches and methods in the use of environmental stress screening and Halt/HASS to markedly improve product quality and life.  Unfortunately, there was widespread misunderstanding and misapplication of the methodology . . . . and some still remains.  Accordingly, we have listed the "Seven Deadly Sins of HALT/HASS". 1. Thermal cycling chamber air instead of product. Environmental chambers with high rates of air temperature change may not qualify as a HALT/HASS chamber.  Simply cycling chamber air temperature is not sufficient.  HALT/HASS requires thermal stimulation of the product. Thermal cycling must cause the product to physically expand and contract at a relative high rate of change over a number of stress cycles.  That is why you cannot simply use traditional environmental simulation chambers or sell them with a "HALT/HASS" label. 2. Vibration levels measured on table instead of product. As in product thermal stimulation, HALT/HASS requires a product vibration response.  Measurement of the input is not measurement of the product response to 6dof vibration. 3. Putting latent defects into product. HASS overstress, whether, thermal, vibration, humidity, or other, can well cause new latent defects, which were not there to begin with. Each product is different.  It is vitally important to determine the optimum stress levels empirically when establishing a HASS production screen. 4. Taking out too much product life. HASS screening during manufacturing can take unneeded life out of a product. If the screen is set too high or the one screen fits all approach. 5. Not tailoring HASS stress to product. It is imperative that the HASS screens be tailored to the product.  The one screen fits all approach does not work.  The screen level may be too low or to high  for some products.  If too low it can  allow potential infant mortality defects to be undetected.  If too high it can take unneeded life out of the product. 6. Not functionally testing product while undergoing HALT/HASS. Intermittent part failures can go undetected unless they are functionally tested while undergoing HALT/HASS.  The level of detectably must be high in order to obtain the results desired. 7. Over design of product as a result of improper HALT. HALT is essentially an exploratory stress test to find part defects and to replace weak parts with robust parts.  However, care must be taken that the product is not subjected to HALT undue overstress and consequential redesign.  Misapplication of HALT can result in an over designed product that is not commercial viable. WE CAN HELP Our long term experience with HALT/HASS seminars, installations, and practitioners worldwide is a valuable resource that we welcome you to draw on. Please do not hesitate to contact us.

The Problem The short lifecycle of today's electronic products creates many pressures for rapid development and manufacture of new products, or product upgrades, in order to stay ahead in the competitive market place. Take for instance, the short model life of computers and printers. A new model appears every few months. Time-to-market is short, and customers expect the new models to work "out of the box" each and every time. These pressures can result in compromised product development and/or manufacturing problems caused by part, process, and workmanship defects. The result is increased manufacturing costs, warranty costs, impacted profit margins, and sadly worse, customer dissatisfaction with resulting loss of market share. The ESS Solution Environmental Stress Screening (ESS), is the solution. It typically utilizes thermal cycling with or without vibration to precipitate latent defects, the so-called "early life defects" which appear during the early life stage of product use. The "bathtub curve" illustrates the life cycle of a product with early life and wear out defects. ESS requires rapid product thermal cycling over a wide temperature range. The objective is to stress components by means of differential expansion rates of the various mounted components, solder connections, and the component mounting assembly itself to precipitate the early life defects. Vibration is likewise utilized to further fatigue the product. Determination of the proper levels are typically determined by increasing environmental stress in step-by-step level. It is an empirical procedure which is different for each product configuration. HALT / HASS HALT/HASS are two applications of the ESS concept. The HALT test is utilized during product development.  It determine initial weakness in the product by increasing stress level in steps to the component destruct levels. Then it replaces weak components with more rugged ones, thereby increasing product reliability. Resulting estimates of improved product life and warranty can be also be accomplished. For example, by applying HALT to a UUT (Pre Halt), we find destruct levels for a given stress-vs-time. By analyzing these failures and then making corrections, we are then able to receive a more robust UUT (Post Halt).  By relating Pre & Post Halt results found in actual use (Field Stress), an estimate of the improved life and subsequent warranty extension are possible. Example of Warranty Improvement Using HALT The HASS process is a production screen to assure that weak components are precipitated (failed). HALT experience and the step stress empirical evaluation is used to establish a good screen. It is important that the level of stress is tailored to the product. There is no one-stress-fits-all. Furthermore,  the product must be functional tested while undergoing stress to detect failures and intermittents. 100% production screening is initially recommended. Subsequently, lot screen sampling may be possible. The HASS screen should be evaluated over time to assure it is doing its job.

Hanse is proud to introduce one of the most advanced integrated touch screen systems on the market. It allows for complete chamber control from the touch panel. It has advanced capabilities including: 12 Channels of Vibration analysis maximum 14 Thermal Couples of input maximum

Why Hanse Environmental builds the best HALT/HASS Chambers on the market. 1. Up to 100Grms 6DoF vibration (US Patent). This is twice that of the industry! 2. 50% reduction in air consumption for vibrators. This is a real cost savings. 3. Three-year unconditional warranty for the vibration system and controller. Best in the industry. 4. New air plenum that reduces electrical and LN2 consumption. Our unique cyclonic airflow results in real utility cost savings. 5.  SCR control of heating elements. Adjusts heating KW to that required by the thermal load and temperature change rate requirements. This reduces electrical usage. 6. We do not use a proprietary controller that is only available from Hanse. We use a Watlow Programmer/Controller affording ready access and support from the Programmer/ Controller manufacturer. Replacements are available worldwide.

Hanse Environmental, Inc. in cooperation with Samwell Testing (China) and Engineering Services (Mexico) held two seminars in China during March 2009. The first seminar was in Beijing on March 17, 2009. The second seminar was in Shanghai, March 20, 2009. Attendees at the seminars represented more than thirty companies who are seeking ways to design and build more reliable products for the markets they serve. Hanse Environmental had a great time introducing the HALT/HASS Systems in China!