REG NASA-LLIS-0429-1996 Lessons Learned Low Strength Solder Joints (~1975).pdf

1、Lessons Learned Entry: 0429Lesson Info:a71 Lesson Number: 0429a71 Lesson Date: 1996-07-15a71 Submitting Organization: JPLa71 Submitted by: J.A. RobertsSubject: Low Strength Solder Joints (1975) Abstract: In the process of reflow soldering flat pack leads to printed circuit boards during the Voyager

2、program, it was discovered that a high phosphorous content in the plating process for the Kovar leads can weaken solder joints. Evaluate the effects of phosphorus when soldering or welding nickel plated surfaces.Description of Driving Event: (Relevant Historical Lesson(s) Learned)While in the proces

3、s of reflow soldering flat pack leads to printed circuit boards during the Voyager program, small black spots were observed on some leads of various CD 4000 series flat packs. Analysis revealed the solder surface of the leads to be poorly wetted, caused by a high phosphorus content in the plated sur

4、face, and the solder joints to be substantially weakened. (Some joints when barely touched, fell apart). As a result, suspect flat packs were replaced, wherever found.The Kovar leads of the flat packs are electroless nickel plated to provide a solderable surface. The plating process, which also copl

5、ates elemental phosphorus, begins to plate a poor solder surface when the phosphorus content exceeds approximately 7% by weight. Since the nickel depletes at a faster rate than the phosphorus, it is necessary to monitor the plating solution and maintain an acceptably low level of phosphorus. Also, w

6、hen a poor solder is found to exist as a result of excess phosphorus, platers will usually overplate with tin to regain a solderable surface. This overplate when exposed to the mechanical and thermal stresses of lead forming and reflow soldering will crack and pull away from the phosphorus rich nick

7、el plate below.Reference(s):Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Part Failure Analysis Report Log 2624Lesson(s) Learned: A high phosphorous content in the plating process can weaken solder joints.Recommendation(s): Evaluate the effects of

8、phosphorus when soldering or welding nickel plated surfaces.Evidence of Recurrence Control Effectiveness: N/ADocuments Related to Lesson: N/AMission Directorate(s): N/AAdditional Key Phrase(s): a71 Hardwarea71 Industrial Operationsa71 Parts Materials & ProcessesAdditional Info: Approval Info: a71 Approval Date: 1996-03-28a71 Approval Name: Carol Dumaina71 Approval Organization: JPLa71 Approval Phone Number: 818-354-8242Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-