IPC-9708 Test Methods for Characterization of PCB Pad Cratering outlines methods of evaluating the susceptibility of materials in a printed board assembly to cohesive dielectric failure underneath surface-mount technology attach pads. IPC explains the test methods described in this standard can be used to rank-order and compare different printed board materials and design parameters.
The three test methods - cold ball pull, ball shear and hard pin pull - enable product developers to determine the best material for their application, IPC says. The standard was developed in reaction to what is known as pad cratering, which IPC describes as "a vexing problem in lead-free assemblies, largely attributed to problems with the resin used to make a printed board."
Satish Parupalli, an engineer with Intel who helped coordinated IPC-9708's development, said, "The standard will help people select, say, four materials that seem to meet their needs. Then they can build test coupons defined by IPC-9708 and run tests on these coupons. That lets them make a decision before they build any real products."
Dr. Reza Ghaffarian is an engineer with NASA's Jet Propulsion Laboratory. He chaired the IPC SMT Attachment Reliability Test Methods Task Group that developed IPC-9708. On the topic of pad cratering, he noted, "In the beginning there wasn't much attention paid to these types of failures because they were almost unheard of." But, he said, as companies started getting products ready to ship they began to realize they had problems with many parts, not just one or two. "These are catastrohpic failures that are sometimes latent," he said. "The defect doesn't always show itself in testing."
IPC says using IPC-9708 will result in cost reductions because it will reduce the burden of verification and qualification.
