Impact strength evaluation of solder joints in BGA by dropping steel rod

The solder joints of ball grid array (BGA) packages in mounted in portable electronic devices like mobile phones suffer mechanical shock when the device is dropped during use. Accordingly, along with developing a quantitative method for evaluating the impact strength of BGA solder joints, improving the strength of these solder joints against such shocks are necessary. In the current work, aiming to establish this quantitative evaluation method, the authors developed an impact-testing procedure based on three-point bending produced by the impact of a drop steel rod on to a printed wiring board (PWB) mounting a BGA package. With the developed test, a PWB can be repeatedly subjected to impact bending deformation in a simple and stable manner. Since the test can reproduce the same mechanical impact as that suffered when a portable electronic device is dropped during use, it is well suited to strength evaluation during the development stage of BGA packages. In the strength evaluation, the maximum value of strain generated in the corner region of the package is used. A strong relationship between the maximum strain and solder-joint strength was found. Moreover, the impact strength of the solder joint depends on the rise time of strain in the PWB, namely, as rise time shortens, impact strength falls.