In March of this year, the Automotive Electronics Council released a validation standard for component products, which targets the most common solder joint cracking failure in automotive electronic product applications.
This article summarizes the typical failure modes of solder joint cracking and compiles the corresponding inspection standards of AEC-Q007 for OEMs such as JDM and GDM.
Analysis of abnormal cracking of solder joints
1,Failure cracking of Lead-Free Solder Joints
During the application process of automotive electronic products, the working and environmental temperatures fluctuate repeatedly.At the same time, the difference in expansion coefficients between the device and the board causes stress accumulation between the solder joints (i.e. non elastic strain accumulation caused by thermal fatigue).
In order to release stress, the lattice direction of softer solder begins to be misaligned and displaced (subgrain boundaries are formed), and with repeated application of fatigue stress, microcracks begin to appear at the grain boundaries and gradually crack into small pieces. Eventually, the grain boundary cracks interconnect and the solder joint cracks.
2,Lead solder fatigue cracking
The characteristic of lead solder that tends to maintain a stable state under the accumulation of thermal and mechanical stress promotes the diffusion and gradual enrichment of lead elements (grain coarsening).
The repeated application of stress also promotes the accumulation of lead, causing the shape to become longer and thinner, while the change in shape leads to a large number of lattice defects on the boundary surface.
The continuous aggregation of the same element ultimately leads to the formation of voids between the grain boundaries of lead and tin. The repeated application of fatigue stress causes the voids to gradually expand and interconnect into cracks, ultimately resulting in solder joint cracking.
3,Abnormal cracking in production process
In addition to the situations where fatigue stress can easily cause cracking, the difficulty in controlling the phosphorus content (too much or too little) in the nickel layer of the plate during the chemical immersion gold production process can lead to a decrease in the stress resistance of the solder joint and a risk of cracking.
Relevant verification standards
Whether it is the fatigue stress that the product can withstand during normal use or the insufficient strength of solder joints caused by process abnormalities.The cracking problem of product solder joints can directly lead to electrical open circuit failure, which is a serious quality failure. Various host manufacturers and industry standards have established relevant verification standards for this:
GRGTEST testing service capability
GRGTEST specializes in environmental reliability testing and certification for automotive and electronic products, with a current inventory of over 1000 units of various professional reliability equipment, and the capability to meet extreme requirements such as liquid cooling and ultra-large chambers. In the automotive and electronic product industry, especially in lead-free process verification, GRGTEST has accumulated rich testing experience and analytical capabilities, covering various fields such as corrosion, electromigration, ionic contamination, tin whisker, warpage stress, etc., while also possessing extensive industry service experience.
