Thank you very much!
          
          Sorry for the vagueness.  It's one of the problems with 
          wanting to know about a subject but having no idea where to 
          start.  That's what I like about this TechNet - "There's no 
          such thing as a stupid question."  Well, at least I haven't 
          been blamed for that yet!
          
          Doug McKean
          
          ____________________ Reply Separator _______________________ 
          Subject: Re: Moisture Testing
          Author:  [log in to unmask] at internet-mail 
          Date:    5/11/96 12:00 AM
          
          Doug.
          I suspect that one of the reasons you have not gotten an 
          adequate response is that your question is somewhat vague.  
          "Humidity" testing can mean a wide range of tests, and will 
          mean different things to different people.  The tests you 
          illustrate on the nylon screw, I would have called a 
          materials compatibility test or a materials characterization 
          test.  
          
          For PCBs and PWAs, there is a great deal of testing done 
          which utilizes high humidity to estimate deleterious 
          effects, either from fabrication or assembly.  Most of the 
          temperature-humidity tests fall into the classifications of 
          burn-in tests (for assemblies), electromigration tests, or 
          surface insulation resistance (SIR).  Tests like hydrolytic 
          stability use exposure to high humidity to test for 
          polymeric reversion on solder masks, potting compounds, etc.
          
          Burn in tests are usually done on finished assemblies.  
          Power is applied and the environment cycles from low temp to 
          high temp under high humidity conditions for anywhere from 
          24 to 48 hours.  A unit which fails such a test would soon 
          fail in the field.  If large scale failures start to occur 
          in such a test, it is a sign that the process ist kaput.  
          Kind of an expensive process indicator.
          
          Electromigration tests are often done on the materials used, 
          such as laminate, solder masks, conformal coatings.  This 
          test incorporates high humidity to test a material systems 
          propensity for metal migration.  SIR testing is similar in 
          it's approach.
          
          For more information, you could look in the Bellcore TR-78 
          specification.  Chapters 13 and 14 cover electromigration 
          and SIR.  The IPC will soon have the final version (as soon 
          as I mail it to Dave Bergman) of the SIR Handbook, which 
          covers the applications of SIR to PCBs and PWAs.  You can 
          look in the IPC-TM-650 manual.  There are 4 methods under 
          2.6.3 that cover SIR testing. Several more cover 
          electromigration.  
          
          Man, I get long winded when I get rolling!
          
          You can take a look at IPC-TR-580, 581, 582, TP-1043, 
          TP-1044 as documents that use SIR to test the effects of a 
          high humidity environment on PWAs.
          
          Burn in tests are usually company specific, so IPC may not 
          have standards or specs on this. (Do they, Mike Buetow?).  
          MIL-STD-202 has a variety of specifications on high humidity 
          testing.  MIL-STD-810 covers the methodology for 
          environmental stress screening, which uses high humidity.
          
          Well, gotta stop, my wrists are starting to unhinge.
          
          Doug Pauls
          CSL
          [log in to unmask]