Strain Measuring Technology in Board Level Assembly Process

Yabing Zou, Daojun Luo, Weiming Li
China Electronic Product Reliability and Environmental Testing Institute
Guangzhou, China

The board level assembly technology which contains soldering and assembling is the key link in the manufacture of electronic products. The quality and reliability of board level assembly process directly affects the quality and reliability of the whole products. This has to consider the impact of the strain on the soldering and assembling process. With the high density package and assembly prevails, and the materials at the transformation of environmental protection laws and regulations, the strain-induced damages in board level assembly process are frequent.

It is well known that the excessive strain can result in various failure modes for different package types, surface finishes, or laminate materials. Such failures include solder joint cracking, trace damage, laminate related adhesive failure (pad lifting) or cohesive failure (pad crater) and substrate cracking. Therefore, characterization of PCBA strain in worst-case is critical to the reliability assurance for electronic products. The application of strain gage test had been improved to be one favorable and effective method to discriminate the hazardous process.

Based on the conversion principle between strain and resistance change, strain gage test is a kind of effective measuring technology, which can be used in the fields such as theoretical verification, quality inspection and scientific research. However, the study on strain measurement for PCBAs in electronic industry has just started, and there are still many unsolved puzzles, whether about strain gage selection or about measurement methodology. To address these problems, this study conducted a deep analysis of the basic principle for strain gage test technology combining with strain-induced damage phenomena of PCBAs. Then the strain gage test was applied to PCBA reliability evaluation during a typical mechanical assembly process. And systematic analysis for some critical problems during this process was conducted, such as the strain gage selection technology, specific operation method and strain data analysis method.

PCBAs and components deformation control using strain gage measurement is proven beneficial to the electronic assembly industry, which can be used as a method to identify and improve manufacturing operations that may pose a high risk for interconnect damage.

This article studied on the application of strain measuring technology in PCBA reliability evaluation, such as the strain gage selection technology for PCBA, specific operation method of strain gage tests during PCBA assembly process and strain data analysis method. Accordingly, electronic process related technical personnel can quickly and reliably establish related evaluation scheme, and continue to identify and control the risky PCBA manufacturing process.

The study on strain measurement for lead-free PCBAs in electronic industry has just started and there are still many unsolved puzzles. Facing to this new and challenging research field, there are many more to explore for PCBA strain/stress damage mechanism and evaluation method.