Lead-Free alloy determination in repair / rework

As a technician that does frequent board level repair / rework some issues have come to mind.

I have been an electronics technician for almost 50 years. In that time I have seen the evolution of electronics from point to point wiring using vacuum tubes and descrete components, through transistor circuitry and on to SMT and other technologies. During that evolution was the development of the various alloys of solder and their drawbacks 60-40, 63-37, multi-core fluxes, lead-free. I hold master and instructor certifications for soldering, in the mid 70's I helped develop the solder standards and techniques for the Navy Nuclear Power program and taught technicians those techniques.

With pre RoHs requirements most if not all of major manufacturers used 63-37 solders and repair rework was easy, one just used 63-37, and it was even acceptable to use 63-37 on 60-40 alloys.

With the adoption of RoHs controls and the subsequent use of many different alloys of lead free solders, (at least 6 I know of), the following comes to mind:

1. Are there compatibility issues mixing between the various alloys of lead-free employed currently in electronics manufactures?

2. How does the technician determine the correct alloy of lead-free solder that was initially used and the correct material for repair, if the manufacturer is unknown?

3. Are there strength reliability issues associated with the longevity of lead-free alloys.

4. Will industry standards be updated to delineate alloy determination or disclosure for high reliability applications?

5. Can alternate methods for the complete removal of lead-free solders and subsequent repair using 63/37 or lead-free alloys be developed?

I am currently dealing with issues associated with the fatigue of solder due to age (30+) years with boards being mounted in fixed positions and the solder stress cracking due to the semi-fluidic nature of solder, thermal, vibrational, and gravitational stresses acting on the components. The components, mainly axial lead capacitors and large footprint op amps (bricks) are literly falling off of the boards because the physical bond of the old solder breaks down. This breakdown is occurring mainly on single sided boards without through plating, although I have seen it occurr on double sided board in high cyclic physical stress enviorments (diesel engine gauge boards), and with a higher age.

I just finished reading a very well done article on the physical strength characteristics of the various lead-free alloys.

Any help with the above items would be welcome. Possibly pressure on the IPC to develop standards and testing for repair / rework techniques.

Pat Goodyear Control Technician (Nuclear) Pacific Gas and Electric

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