Requirements for immersion silver on PCBs

This newly revised specification sets the requirements for the use of immersion silver (Iag) as a surface finish for printed boards, adding a maximum deposit thickness based on performance criteria; the minimum thickness requirement was provided in the original release of IPC-4553. Revision A also establishes a single thickness range to avert confusion between what is “thin” and “thick.” “While the maximum thickness requirement may seem like a relatively simple item to generate, it took a great deal of effort on the part of the 4-14 Plating Processes Subcommittee to define the hard number of what the maximum thickness can be to produce a high quality surface finish,” says Subcommittee Co-chair Gerard A. O'Brien, president, Solderability Testing & Solutions, Inc. O’Brien notes that the lack of a maximum thickness requirement in the original release of the document in 2005, confounded with the “need to know” of whether the Iag being used was of the “thin” or “thick” variety, could easily mislead a user to apply the finish outside its optimum process window. He adds, “This, in turn, could result in an inferior finish quality that would not perform adequately during subsequent assembly.” Image source: AT&S