The influence of solder joint voids on reliability is complicated. The position, size and quantity of voids have different effects on the reliability of solder joints of different structures. The industry has not yet made a clear conclusion. There is only one acceptance criterion for voids in BGA solder joints in the IPC standard. Therefore, the focus here is on the acceptability of BGA solder joint voids. Reliability studies of BGA solder joints have shown that small-sized voids may be beneficial to solder joint reliability, which can prevent crack propagation, but voids at least reduce thermal and flow-through capabilities, and BGA reliability is disadvantageous. Impact.
Before discussing the acceptable conditions for voids for BGA solder joints, first understand the type of BGA solder joint hollow:
(1) Macrovoid: This is the most common void phenomenon caused by the evaporation of flux trapped by the solder. Such voids generally have no effect on reliability unless they are distributed near the interface.
(2) Planar Microvoid: A series of small holes are located between the solder and the PCB pad interface. These holes are Cu under the surface of the Im-Ag. Caused by the hole. They do not affect the early reliability of solder joints, but they can affect long-term reliability.
(3) Shrinkage Void: It is formed by the solidification shrinkage of solder. Most SAC solders and other lead-free solders generally shrink when they solidify. Such voids generally do not appear at the PCB-to-pad interface and do not affect reliability (there is no possibility that cracks spread to the interface between the solder and the PCB).
(4) Microvia Void: Appears on the micro-blind hole of the PCB pad. If this design is located in a solder joint with a relatively high stress, it is an impact on reliability. It can be solved by electroplating.
(5) IMC Microvoid: It is easy to appear between Cu and high-tin alloy. It does not appear immediately after soldering. It occurs during high temperature or high temperature cycling. The reason is not clear, it has an impact on reliability.