ye and pry testing (also called "dye penetrant test") reveals hidden discontinuities beneath SMT components. Although destructive, dye and pry test is the most efficient and cost-effective means of verifying 100% of solder connections under BGA and other bottom-terminated SMT packages. It can also be used to confirm cracks or leaks on sealed SMT parts.
Sample preparation typically begins with excising the portion of the board containing the target feature. PSI uses a specialized saw blade engineered for precision cutting of circuit boards. It is crucial to use the proper equipment and technique for this initial step, as vibration or shear forces could compromise the integrity of the sample and introduce novel defects.
Next the sample is immersed into a low viscosity dye, inside a vacuum chamber. Capillary action pulls the liquid dye into every crevice and void, assisted by the pressure differential created by the vacuum. After dye immersion, the sample is baked dry in a moisture removal oven, then carefully fixtured in a puller assembly to separate the component from the board. Board and component are then examined under a microscope, where defects and anomalies are recorded and imaged.
Both methods are useful tools for process validation and failure analysis of bottom terminated components, but which is suited for your project? For failure analysis, it's often beneficial to begin with X-ray, CT X-ray, and/or visual microscopy, which preserve the sample intact. If destructive analysis is still indicated, there are several questions that might inform the investigative strategy, such as...
If the goal is process validation, the questions are a little simpler, and often driven by end user requirements. A determination needs to be made as to how many boards, and for each board, how many of each type of SMT connection need to be examined. Here's a helpful summary for positioning the methods:
Dye and Pry
Lower cost per joint
Modest amount sample prep time
Look at 100% solder connections at once
Limited data ("yes or no" opens, see horizontal point of separation)
Longer sample prep time, potting and multi-step polishing process
Look at one row of solder connections per cross-section. Requires choosing the best target plane.
Detailed data (intermetallic layers, fracture propagation path, voiding, grain structure, solder wetting angles)
For help with your investigation, contact the solder experts at Process Sciences.
Microsection | Cross Section | BGA Analysis
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