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February 1999

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Subject:
From:
Richard Philp <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Wed, 3 Feb 1999 09:50:13 PST
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          Dear Technetters,

          In the good old days we used to thermally shock boards - literally
          move from a hot oven to a freezer via a conveyor belt with no real
          control of the ramp rate.

          We then improved the process and carried out extensive (and expensive)
          environmental stress screening of our boards.  This has involved
          temperature stressing at about 20 degrees per second to about 70C with
          functional testing during the temperature ramp.  This was followed by
          an hours soak with more testing and then ramping to about -30C with
          yet more testing.

          We are now investigating the use of HARASS, Highly Accelerated Rapid
          Air Stress Screening, which gives rates of 60 C/sec and very
          controlled top and bottom temperatures.  This technique is supposed to
          make weak joints apparent so that testing can be carried out after the
          test.

          Has anyone any experience of this technique?  There is a concern that
          it may damage components but we have found no evidence.

          Thanks for any information,

          Richard Philp

          Matra BAe Dynamics,
          Stevenage,
          UK

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