Board-level Package Bonding Materials Impact On Solder Joint Reliability Of Ctbga Components

Electronic products have full access to lead-free era along with the implementation of Restriction of Hazardous Substances (RoHS) in European Union and《Regulation on contamination control and management of IT products》in China, the size and solder ball pitch of advanced micro electron seal forms such as Thin ChipArray Ball Grid Array (referred to as CTBGA) are getting smaller, playing such advanced packaging size), solder spacing narrower, plus the brittle of lead-free solder joints, board level adhesive materials must be used to release stress, and provide long-term protection for components. Strong market demand driven adhesive materials technology gradually increase, more and more adhesive materials was developed. In order to realize best reliability of the specific electronic products by adhesive materials technology, the research work for the influence of different adhesive materials to solder joint reliability is become more and more urgent.This paper studies the influence of current commonly used eight kinds of adhesive materials (involving the bonding patterns of full underfill, partial underfill, edge bonding and corner bonding) to mechanical bend, shear, drop and temperature cycle reliability of CTBGA assembly solder joint, and obtained as follows achievements:(1) The reliability test shows that adhesive materials improve the mechanical bend, shear and drop reliability of solder joint by 29.7%, 27.0% and 60.0 times in average, however, the reliability of temperature cycle is reduced by 32.7%. The improvement of mechanical reliability from material buffer or absorption effect to mechanical stress, And coefficient of thermal expansion (referred to as CTE) increase sharply when the environmental temperature is higher than its glass transition temperature, the CTE mismatch between adhesive materials PCB and solders lead to premature failure of solder eventually.(2) The failure analysis test to the sample which after reliability test shows that:For mechanical bend test, solder joint failure region in the left and right movable anvil was symmetrical distribution, and the vast majority of solder joint fracture locations occur in the junction of PCB pad & PCB substrate. For shear test, solder fracture position more concentrated at the interface of PCB pad & PCB substrate and the interface of components pad & solder, and presented as the fracture locations with the volume of adhesive materials increased gradually change from the former to the latter. For drop test, solder fracture position more focus on the interface of components pad & solder, While the solder fracture positions in temperature cycle test are in the solder joint which is close to PCB pad and components pad, and fracture interface presents different from the brittle fracture of former three forms, but is fatigue fracture.(3) Through the finite element method simulates the stress and strain state of solder during the reliability test,3D finite element of elasticity, plasticity and creep model proves the stress concentration exist at fracture position.This research work on the various adhesive materials quantitative evaluation to application performance and the effect for solder joint reliability, it has important significance for the enterprises to pertinently choose suitable adhesive materials.