Chris,
This is probably one of the reasons medical equipment and implants are exempt from the directive.
Below a quote from an article published by the medical device network.
RoHS excludes medical devices (category 8) and monitoring and control instruments (category 9), due to concerns over the reliability of substitute materials, particularly of lead in solders, in safety-critical equipment. The directive states, however, that the European Commission will present proposals for including these categories at some point in the future.
I assume that the last sentence is the reason you look into lead-free now.
I�m not familiar with the IEC - 60601 test, only with Bellcore electromigration which is 85RH/85C 500 hours.
Is the test pattern similar to the IPC-B-25? You specify 95%RH but what is the temperature in the test chamber and voltage supplied to the test coupons? Does this test include pH, copper mirror and silver chromate paper test (presence of halides) for the flux? Also do you have restrictions in alloy selection?
Does the test coupon with the lead-free solder wires you tested show filament growth?
Answering these questions would let me know if I can help.
Patrick
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