Blistering on plastic edge connectors

Blistering is a term used in the industry to describe the blister effect that occurs on plastic parts ­– in this case on plastic edge connectors, as can occur with automatic soldering. In some cases the effect can be tolerated up to a certain degree, but if it is accompanied by a significant loss of dimensional stability, entire subassemblies can, in a worst-case scenario, become rejects. This example deals with a defect in series production, in which the blister effect made it impossible to properly assemble casing covers in the subassemblies. 

• Macroscopic and microscopic documentation of the defect
• Thin-section preparation of previously embedded products
• Examination of the thin-section samples in a bright field under a light microscope

The affected edge connectors have blisters on the surface. A higher magnification reveals unsatisfactory forming of the surface, pointing to the process temperature being too low. The cross-section of the component shows nest-like cavities within the edge connector, which are essentially voids resulting from the production process. Through the effect of high temperatures during mechanical soldering, any molecule orientations already existing in the part can relax, resulting in the delamination of boundary layers and thus leading to the blister effect. In this case, the proportion of cavities in the part was so large that defective edge connectors were identified gravimetrically during the production process. 

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