Hot Bump Pull Test: Solder Bumps & SMD Pads

Hot bump pull and hot pin pull test is used as a method to evaluate the cohesive adhesion underneath SMD device pads to test for cratering, interface and material failures.

The latest pad cratering standard, IPC-9708, defines hot bump pull as a method to evaluate the susceptibility of printed board assembly materials and designs to cohesive dielectric failure underneath surface mount technology attach pads.

A common failure mode in lead-free assemblies is pad cratering, where failures often occur post assembly and is caused by the contact pad on a PCB or package substrate lifting away. Typically, the failure results from an overstress condition induced by manufacturing, test and handling. Proper design, materials selection and stress limits are required to limit this type of failure.

Because this failure is inherently mechanical, it cannot necessarily be detected through ICT or other function electrical tests. Hot bump pull test can be used to characterise these failures and determine correct process, materials and setup parameters.

The principle of hot bump testing, is to position a copper pin so that it is touching the solder bump being tested. The test is then executed, where the pin temperature ramps up according to the defined temperature profile created. At reflow point of the solder, the pin drops down to a desired level, ensuring a good solder joint. The pin is then clamped and the solder cooled until it reaches a defined temperature, the pull test is then automatically executed, recording the force-time, force-distance and energy values.