Dr. Bob on Gold Flash Contact Finishes (and Max Peel)
To honor his former colleague Max Peel, who passed away in April, Dr. Bob discusses gold flash contact finishes and the warning that is Peel’s Law.
This article will eventually be about gold flash contact finishes, but it begins with a few words about my colleague Max Peel. Max passed away on April 16 of this year, after a long struggle with cancer. He will be missed by many in the connector industry – those he referred to as “gray beards” (of which I am one), and by many who never met him but have benefited from his contributions to the connector industry.
His involvement with connectors began at Burndy Corporation in 1959 where he got his experience in connector design before moving on to Texas Instruments, where he continued his design work, and left as manager of advanced development and testing techniques. Max then became founder and president of Contech Research, an independent test laboratory that specializes in connector testing and failure analysis. In the interim, he made many contributions to the connector industry through his participation in the EIA 2.0 Committee on Connectors and Sockets. Max was an active and outspoken member of that committee and its subcommittees for more than 30 years – active in that he made many contributions to the test procedures used by the connector industry today and outspoken because that was Max. Max received the Lifetime Achievement Award from IICIT in 1992 and the ECIA Distinguished Service Award in 2011 for his contributions to the connector industry. He will be missed.
Max always enjoyed a technical discussion and instigated many of them himself. I participated in many of those discussions as a representative of AMP Incorporated and as Max’s co-presenter in presentations of the IICIT course “Connector Basics,” starting in 1994 and continuing as a consultant after I retired from AMP in 1998. This article revisits one of those discussions: Gold flash contact finishes.
Max delighted in presenting “Peel’s Law,” which states that anyone who makes, specifies, buys, or uses gold flash finishes deserves all the problems they’re going to get. Pure Max.
Max and I usually, but not always, agreed on technical issues, but often disagreed (usually agreeably) on language, with me being the academic Dr. Bob and Max being Max. Gold flash finishes are one of the subjects we agreed upon. This article utilizes Dr. Bob’s academic version, not Max’s more colorful style (although I did try to lighten up a bit).
First, some background: A major reason for using a contact finish, whether it is gold or tin, is to protect the contact interface from the ingress of contaminants resulting from corrosion products of the copper alloy contact spring. Gold is a noble metal, so called because it is essentially immune to corrosion and, when properly applied as a contact finish, provides the desired protection. The key words are “properly applied,” which includes coverage of the contact interface and the ability to maintain that coverage through the number of mating cycles intended in the application (but more on that later). A gold contact finish, however, also should include a nickel underplate, which provides additional benefits outside the scope of this article.
As gold prices rose in the late ‘70s and early ‘80s to (gasp!) $800 per ounce, reduction in gold usage/cost became a major issue to connector manufacturers. In the ‘70s, gold plating thicknesses were as high as 100 microinches and contacts were essentially plated with gold overall. Two ways to reduce gold costs, therefore, were by selective plating of gold only at the contact interface and reducing the gold thickness (that’s where the nickel comes in).
Selective plating practices improved dramatically and gold usage was reduced with minimal effects on performance. Reducing the gold thickness was a more challenging issue because the potential for impacting performance was much higher. Thicknesses were reduced to 50, then 30, then 15, and finally to flash. And Peel’s Law eventually came to be.
To be “properly applied” (that is, to do its job), the gold plating must cover the contact interface. As gold thicknesses decreased, porosity (small defects in the gold plating that could act as corrosion sources) became an issue, and plating techniques were improved dramatically to reduce such porosity. A major issue with flash gold is that it does not necessarily provide complete surface coverage, much less controlled porosity, because a “flash” can range from a few to several microinches, and thus may not do its intended job of protecting the contact interface from corrosion product contamination. Another issue, not surprisingly, is that gold flash, due to its low thickness, will have limited durability. With that background, we return to Peel’s Law.
The first topic in Peel’s Law is “makes,” that is “plates,” a gold finish. Two concerns here: controlling the gold thickness at a few microinches is difficult, to say the least, and measuring the thickness is also difficult. X-ray fluorescence, the dominant method of plating thickness measurement, measures mass, not thickness. As noted above, at flash thicknesses the uniformity of surface coverage becomes an issue so the correlation of mass with thickness becomes problematic. Needless to say, the plating quality at flash levels is highly supplier-dependent.
The second topic is “specifies.” I have heard of, I hope apocryphally, ”gold color” as a specification, “flash” with no thickness requirement, and thicknesses from one to five microinches. The surface coverage can vary dramatically over that range of thickness. A second aspect of “specifies” arises from the manufacturer and user perspectives: How much flash is needed for a given market or application? Good luck with that.
Third comes “buys,” referring to the buyer/engineer interaction. Engineering has the specification and supplier problem, and the buyer has the “but-I-can-get-it-cheaper” temptation. Woe to all if he succumbs at the flash level.
Finally we get to “uses” – the point where all involved get to point fingers at one another. The end-user component engineer (if there still are such people), “challenged” by management to reduce costs, insists that the connector product engineer specify the minimum gold thickness (whatever that is and whomever he gets it from). And there you have it: “All the problems they’re going to get.”
It must be said that there are many gold flash finish connectors performing satisfactorily in the field; but I suggest that this is more an indication of the intrinsic robustness of the redundancy of asperity contact interfaces, with an appropriate contact normal force, than a validation of gold flash finishes as such.
Max delighted in citing Peel’s law and telling stories about gold flash failures. So, in honor of Max Peel, let’s now pour ourselves a nice glass of scotch and light a cigar.
- Nanocrystalline Silver Alloy Contact Finishes in Electronic Applications - April 6, 2015
- Nanocrystalline Silver Contact Platings - March 16, 2015
- Dr. Bob on Gold Flash Contact Finishes (and Max Peel) - September 22, 2014