Over the past few years, pad cratering has become a vexing problem in lead-free assemblies, largely attributed to problems with the resin used to make a printed circuit board. To help industry eliminate the defect and, at the same time, cut costs, IPC has released IPC-9708: ‘Test Methods for Characterisation of PCB Pad Cratering.’ The new industry standard provides three standardised test methodologies that enable product developers to determine the best material for their application.
“In the beginning, there was not much attention to these types of failures because they were almost unheard of,” says Dr Reza Ghaffarian, a NASA Jet Propulsion Laboratory engineer and the chair of the IPC SMT Attachment Reliability Test Methods Task Group that developed IPC-9708. He explains that as companies started getting products ready to ship, they began to realise they had a problem that was not with just one or two parts, but with many. “These are catastrophic failures that are sometimes latent. The defect does not always show itself in testing.”
IPC-9708 provides test methods to evaluate the susceptibility of printed board assembly materials and designs to cohesive dielectric failure underneath surface mount technology (SMT) attach pads. The test methods, which include cold ball pull, ball shear and hard pin pull, can be used to rank order and compare different printed board materials and design parameters. “The standard will help people select, say, four materials that seem to meet their needs. They can then build test coupons defined by IPC-9708 and run tests on these coupons,” says Satish Parupalli, an Intel engineer who helped coordinate the development of the IPC-9708 within the IPC 6-10d task group. “That lets them make a decision before they build any real products.”
Companies that use IPC-9708 can also expect substantial cost reductions by reducing the burden of verification and qualification. As is the case with many standards, widespread adoption would bring significant benefits to industry. Proponents hope that resin suppliers and board fabricators will begin reporting data based on standardised testing.
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