Forum: Reliability & Maintainability Questions and Answers

Topic: Reliability & Maintainability Questions and Answers

Topic Posted by: Reliability & Maintainability Forum (src_forum@alionscience.com )
Organization: System Reliability Center
Date Posted: Mon Aug 31 12:47:36 US/Eastern 1998

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Original Message:

Posted by: Glen Hanington
Date posted: Mon Mar 5 15:21:34 US/Eastern 2007
Subject: Reliability Testing
Message:
We have a problem. We've built up very large number of printed wiring assemblies before we discovered that the board itself has a problem. There are 2 pad areas on the board that form connection points to copper busbars. Each pad is 1/2" x 1/2" in area, solder coated, with a 0.150" hole near the middle. A 6-32 square-cone SEMS screw passes through this hole from the back side of the board and screws into each one of the 2 busbars. The hole is plated through and the back side of the board has an identical pad as on the front of the board. The problem is this: solder mask covers both pads except for a 0.250" diameter circle around the hole on both sides of the board, preventing full surface contact with the busbars. Some of our product models have 83 Amps of current pass from the board through each busbar. We've experimented with removing the solder mask, but that isn't possible due to the other components already on the board. I've been tasked with developi! ng a reliability test to prove that if we were to use these boards we would not have a reliability issue in the field. How would you recommend that I go about performing this test? As I see it, this will involve the combined stresses of current, humidity, and vibration. Is there some way to set up this test, or series of tests, to prove that this will not be an issue within our 5-year warranty period? It is also believed that about 1500 of these boards are in the field, but there have been no reported failures as a result of this issue.

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