Solderability and tinning: does the industry really know the difference?: Page 3 of 3

January 25, 2016 // By Joseph Federico
For many years NJMET has had the wonderful privilege of providing the electronic component industry with tinning and solderability services in the aerospace, military and medical fields. A particular dilemma which continues today is understanding the purpose of each service.
When to use solderability testing

Solderability testing is a great tool to use to help determine if the surface finish of the selected components will provide the degree of wetting necessary for acceptable solder connections. For instance, if solderability testing results indicate less than optimal solderability, it could result in poor wetting and defective solder connections requiring rework and additional processing. Solderability testing can also be used to determine the effects of the storage conditions on the surface finish. By including accelerated aging, the testing can also estimate acceptable storage life. The testing can also be used to verify conformance of the components as received from the vendor.

When to use tinning

When you want to ensure you get the best wetting on your solder connections, you should tin the terminations just prior to the soldering process. Jim Raby, one of the pioneers of our industry and the founder of STI Electronics once said, “nothing solders like solder.” Pre tinning just prior to the soldering process ensures that the Solderable terminations have a pristine solder coating that has not had a chance to form an oxide layer on the surface. This used to be a very common process for the manufacturing of high reliability electronic assemblies. When pre tinning is accomplished just prior to the soldering process it eliminates the need for solderability testing.

Tinning is also the best method to rework terminations that exhibit degraded solderability. Even severely oxidized terminations can be reworked by a hot solder dip tinning process replacing the oxidized surface with a pristine solder finish. Tinning in a tin lead solder bath is one of the methods used for lead free terminations that have to be used in a tin lead soldering process. The risk of whisker growth is greatly diminished by replacing the lead free finish with a solder finish that contains lead.

To summarize, tinning services should be selected:

  • When it’s necessary to replace a lead free surface finish.
  • To rework terminations that no longer meet the solderability requirements.
  • To ensure that the most solderable surface is available.

Solderability testing services should be selected:

  • To verify vendor conformance with solderability requirements.
  • To verify the storage conditions have not degraded solderability.
  • To estimate the long term effects of storage.

Acknowledgements:

I would like to acknowledge the Legendary Mr. Jim Raby as well as Dave Raby, Ray Cirimele and Marietta Lemieux from STI Electronics, Inc, 261 Palmer Rd. Madison Alabama (256) 705-5517(256) 705-5517 http://www.stielectronicsinc.com/

My sincere thanks to all of you for your wonderful help, insight, photos and encouragement with this article.

About the author:

Joseph Federico is Vice President of NJMET Inc - www.njmetmtl.com