Techneters

   How I can qualify a process involving different materials with different
CTEs.

   Scenario:
   One component soldered to the board with thermal bond underneath and
conformal coating

   This board will be outdoors and will face wide temperature range (
winters and summers )

   I don't have all numbers yet, but would like to known how to analyze them
when I got all info.

   CTE of the board ( metal substrate type board for better thermal transfer
characteristics )
   CTE of the solder joint
   CTE of the thermal compound underneath the part ( approximately 1 mil
thick )
   CTE of the conformal coating

  Tg of the board
  Tg of the solder joint
  Tg of the thermal compound
  Tg of the conformal coating

  Question :
   What is the safest CTE mismatch that would not affect solder joint
reliability ?

  Thanks for any advice.

Jorge Santana
Manufacturing / Process Engineer
LWT

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