Solder-Related Defects

The 2D x-ray systems are very effective in testing single-sided assemblies. With the use of a sample manipulator, an oblique view angle enhances inspection of both single- and doublesided assemblies with some loss of magnification due to increase in distance between source and detector. Experience is needed in discerning between bottom-side board elements and actual solder and component defects. This can be very difficult or impossible on extremely dense assemblies. As discussed previously, certain solder-related defects such as voids, misalignments, solder shorts, etc. are easily identified by transmission systems. However, even an experienced operator can miss other anomalies such as insufficient solder, apparent open connections, and cold solder joints. 

Solder dispensing is integrated into the placement process flow, minimizing related defects. 

In most factories, defect levels at the wave step are higher than those for the oven mass reflow process. The defects are related to poor process setup, poor process control, inadequate PWB design, or any combination of the three. Although wave soldering has been around for a long time, it is stiU not very well understood, due mainly to varying machine configurations and number of process variables. 

In addition to termination-material or compatibility issues, there are several other component material-related concerns, the most important of which is damage due to moisture uptake when processed at the higher Pb-free assembly temperatures. The most prominent defect is delamination due to warpage or popcoming, a phenomenon whereby the moisture absorbed by a component on the manufacturing floor is converted to steam when exposed to the solder reflow-temperature cycle. Many components are downgraded in moisture-sensitivity-level rating when used with lead-free process conditions. 

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