Abstract:
In the process of reflow soldering flat pack leads to printed circuit boards during the Voyager 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 process 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 surface, 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 coplates 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, when 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 nickel plate below. - Reference(s):
- Part Failure Analysis Report Log 2624
Lesson(s) Learned:
A high phosphorous content in the plating process can weaken solder joints.
Recommendation(s):
Evaluate the effects of phosphorus when soldering or welding nickel plated surfaces.
Evidence of Recurrence Control Effectiveness:
N/A
Documents Related to Lesson:
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Mission Directorate(s):
N/A
Additional Key Phrase(s):
- Hardware
- Industrial Operations
- Parts Materials & Processes
Additional Info:
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