Ask the Experts
May 16, 2024 - Updated
June 24, 2014 - Originally Posted

Class 3 Pin Contact Question

I am working on a class 3 product. We have an assembly from one operation that has a tinned pin. The pin is inserted into a gold plated socket on the next assembly.

This bothers me to no end but no one on the program seems to care. Does this meet class 3? What do you say?


Expert Panel Responses

This sounds like a design issue.

On the one hand, if the tinned pin was originally gold plated, the gold plating is required to be removed in the area of the solder joint. But if the pin is soldered to a plated through hole, then the tinning must only take place in the area where the solder joint will be formed, and while this can be done by masking the mating end of the pin to retain the gold on the mating area, it is somewhat labor intensive. But putting a completely tinned pin into a gold plated socket is a bad practice, whether the J-STD-001 allows it or not.

Eventually the tinned pin will oxidize, and the connection to the gold brushes in the socket will be lost. While this is no big deal if the device is a consumer product, it is a big deal on a high-reliability device and as such it should be corrected. You may wish to notify the design engineer of the issue.

It is quite possible that he/she never intended to have the tinned pin mated into the contact, and the manufacturing engineer does not realize that the process documentation must clarify how the pin is supposed to be tinned. The manufacturing engineer may not even understand why this is a potential issue.

You may wish to approach them together and express your concern, and let them know that if this is a Class 3 CCA where the electrical connection could possibly endanger lives, they are looking at a potential liability issue. Then they might listen. Mention Chevy Ignition Switch, and see if they twitch.

Richard D. Stadem
Advanced Engineer/Scientist
General Dynamics
Richard D. Stadem is an advanced engineer/scientist for General Dynamics and is also a consulting engineer for other companies. He has 38 years of engineering experience having worked for Honeywell, ADC, Pemstar (now Benchmark), Analog Technologies, and General Dynamics.

This will either not be a problem, accelerate fretting behavior or introduce a cold weld with a high resistance due to the formation of tin-gold intermetallic. So, a 1 out of 3 chance that it will work.

Dr. Craig D. Hillman
CEO & Managing Partner
DfR Solutions
Dr. Hillman's specialties include best practices in Design for Reliability, strategies for transitioning to Pb-free, supplier qualification, passive component technology and printed board failure mechanisms.

This is a design issue and any and all design issues override the Classes of assembly as defined by IPC documentation. The IPC classes as defined are for the assembly of those products not the design, so in reality the classes have nothing to do with the design.

For example the designers may ask for certain issues like plating thickness to meet the reliability requirements of their product, or thicker solder joints, but those are manufacturing issues.

As for putting a tin pin into a gold plated socket contact is not necessarily a good thing to do due to dissimilar materials. Additionally any vibration may cause fretting corrosion which would make the connection intermittent and cause it to fail.The contact and pin materials should be the same for a reliable connection.

Leo Lambert
Vice President, Technical Director
EPTAC Corporation
At EPTAC Corporation, Mr. Lambert oversees content of course offerings, IPC Certification programs and provides customers with expert consultation in electronics manufacturing, including RoHS/WEEE and lead free issues. Leo is also the IPC General Chairman for the Assembly/Joining Process Committee.

Reader Comment
For class 3, all interconnects need to be gold on gold. I seriously doubt that the interconnect of dissimilar metals would pass qualification requirements. In the long term, failures would begin to occur especially in humid conditions. There are several tables that suggest that galvanic corrosion will occur if these two metals would be in contact with each other.

Any tinning of a contact would have to be confined to that area of the contact that needs to be soldered. Not the interconnection between them.

If no one cares, in time problems will occur and the issue will have to be addressed.
Bill Kasprzak, Moog Inc.

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