Defect of the Month

Bob Willis

Be sure to optimize the preheat to improve wetting.

This month we we illustrate high-temperature soldering of through-hole connectors. In this case both the PCB nickel/gold surface and the tin surface of the pin were perfectly solderable. The time to preheat the board and connector before soldering was not optimized for robotic soldering, however. To obtain the correct process setting, balance all settings, but to increase throughput in an inline process using a robot, many applications require preheating. Robots are flexible, but an operator can see and judge the time required.




Read more: High-Temperature Soldering of Through-Hole Connectors

Bob Willis

Soldering in nitrogen or vapor phase environments can increase the likelihood.

Subtle component lifting can be an issue to find during inspection. Most modern AOI systems should be able to detect drawbridging on small passive and active parts. Old systems may struggle with defects like the two shown in FIGURE 1.





Read more: Root Causes of Component Lifting

Bob Willis

Get the right stencil for the job.

This month we illustrate an example of what appears at first glance to be poor lead solderability. When examined, however, it is a combination of component and pad design.

FIGURE 1 shows the lead to be floating in the solder joint, suggesting poor wetting. When we examine the component lead and plastic body, however, the lead is not parallel, so it always sits off the pad surface, even if perfectly soldered. The lead sits in a cavity in the component body to maintain its position. But with the size of the pad used in the design and a full solder paste print, the component body will always lift.


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Read more: Component Body Lifting

Bob Willis

Is poor stencil design the culprit?

This month we illustrate solder balling and incomplete reflow when reflowing through-hole components with pin-in-paste.

Solder balling pin-in-hole reflow (PIHR) close to the body of the connector suggests poor design of the stencil for this application (FIGURE 1). There is no standoff on the corner of this part, which may have permitted the paste to be displaced when the component was attached. There should always be free space around the paste deposit to permit placement and reflow, without contacting the paste.



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