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For its latest revision, the task group behind IPC-SM-840D, “Qualification and Performance of Permanent Solder Mask,” focused on terminology, consolidation, the Pb-free dilemma and test methods.

In a recent interview with Circuits Assembly, longtime task group chair Dave Vaughan, marketing manager, Taiyo America, noted that revision D began simultaneously with the Solder Mask Handbook. In fact, it began with the term “solder mask” itself.

“People were using different terminology for the same product. We did research for the proper term,” Vaughan said. Three terms were being used for the same concept: soldermask, solder resist and solder mask, the last of which the task group adopted. “Predominant usage is ‘solder mask,’ ” said Vaughan, “so we adopted it and standardized” on the term.

Another focus for this revision, according to Vaughan, was removing references to items that didn’t relate to actual product performance. “The C revision was one of the first to minimize the amount of tutorial information on the performance standard. Major portions were devoted to the difference between liquid and dry film solder mask. It should not matter what kind of mask it is,” he stated. Therefore, the team took the next step and eliminated tutorial information from the document.

It also simplified two types of qualifications for the solder mask supplier; it combined material qualifications and material board qualifications with regard to vendor testing requirements to make the document more user-friendly.

Also of great import for this revision was including types of products for Pb-free soldering. In the C revision, for the solder mask specification, “conditions (primarily temperature) were not adequate to determine if products were satisfactory for Pb-free soldering,” said Vaughan. Temperature requirements are higher for Pb-free, so the group added testing at higher temperatures to account for it. Vaughan added, “This was a major request. The Pb-free task force came up with a recommendation for us, and we adopted a similar qualification.”

This was one of its greatest challenges. In defining the process to qualify for Pb-free, the group had the difficult task of determining a process that was “doable by the average supplier and test lab,” said Vaughan. “Most test labs and suppliers don’t have access to equipment to perform multiple passes through the reflow oven.” The task group conducted an evaluation with various companies, running an equivalent number of solder dips in solder pots at similar temperatures. The result was a reasonable equivalent to which no one objected.

Vaughan noted, “When you test for various parameters, you have to use test methods.” It reviewed every test method called out in the document and revised several for which the solder mask task group is responsible; created methods based on ones developed in conjunction with other groups, taking ownership of the new methods; and wrote two new ones.