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A Word to the Wise — Don’t Be Misled By Poorly Viewed Solder Joints

Smaller packaging and considerably reduced PCB real estate is placing greater customer attention on lead-free solder joints. And in many cases, concerns — and even becoming alarmed — over what is seen in highly magnified views can be misleading and unproductive. If solder joints meet IPC-A- 610 Standard, Class III, they are good to go.

In short, IPC-A- 610 STD Class III states that lead-free solder joints are acceptable when solder connections indicate evidence of wetting and adherence where the solder blends to the soldered surface. The solder connections should have a generally smooth appearance.

But sometimes, when a component and its solder joints are ultra magnified, a customer gets alarmed over seeing what they consider to be a defective lead-free solder joint. And this happens a lot in the industry.

Sometimes, the misinformed viewers place solder joints in this suspicious category because the solder is hazy or dull – a characteristic of lead-free solder compared to the shiny finish of leaded solder joints.

So, here’s a case in point, as shown in Fig. 1. The customer rejected this PCB project because there was inadequate solder fillet on several of the connectors. A solder fillet is defined as the concave area filled with solder in the solder joint under the lead of a component.

After magnifying and looking at this solder joint from one view, the customer stated that he “was not seeing all the fillet he should be seeing.” That raised some red flags in his way of thinking. The customer certainly felt the solder joint posed a latent failure and wouldn’t withstand the rigors of actual use in the field.

Assembly engineering and quality control put this project a thorough 100% inspection with different views at different magnifications and measured the solder joints against IPC Standard. It was learned there were no issues with the lead-free solder joints. The project met IPC-A- 610 Standard, Class III.