Soldering Problems

The ideal solder joint for through-hole components should have a wetting angle between 40 and 70 degrees from horizontal, and a smooth, shiny and concave surface. However, it’s really not easy to do. And we always face the following soldering problems.

Stray solder spatters: These bits of solder are held to the board only by sticky flux residue. If they work loose, they can easily cause a short circuit on the board. Fortunately, these are easy to remove with the tip of a knife or tweezers.

Lifted pad: Sometimes you can see a solder pad detached from its circuit board’s surface. This most often occurs when try to de-solder components from the board. The simplest way to repair is to fold the lead over to a still-attached copper trace and solder. Other alternatives are to follow the trace to the next via and run a jumper to there.  

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Common Soldering Problems

The ideal solder joint for through-hole components should have a wetting angle between 40 and 70 degrees from horizontal, and a smooth, shiny and concave surface. However, it’s really not easy to do. And we always face the following soldering problems.

Overheated joint: Sometimes we may have an overheated joint, and that is because the solder has not yet flowed well and the residue of burnt flux cause troubles in fixing this joint. Actually, we can prevent this issue by properly prepared, such as a clean and hot soldering iron, and clean joint timely. 

Too much solder: This might be a perfectly good joint, but it is entirely possible that a blob of solder wets neither the pin nor the pad and is not a reliable electrical connection. If it happens, to draw off some of the excess solder with the tip of a hot iron is a good method. In extreme cases, a solder-sucker or some solder wick can be helpful as well.

Untrimmed leads: Leads that are too long easily cause short circuits. It would not take much force to bend that lead over to touch an adjacent trace. However, it is not difficult to tackle this issue, just to trim all leads at the top of the solder joint.

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Insufficient Wetting

Wetting is the ability of a liquid to maintain contact with a solid surface, resulting from intermolecular interactions when the two are brought together. The degree of wetting (wettability) is determined by a force balance between adhesive and cohesive forces. Wetting is important in the bonding or adherence of two materials. So what’s the result of insufficient wetting? Here EPCB lists 3 examples. 

Insufficient Wetting (Pad): Suppose a solder has wetted leads nicely, but it has not formed a good bond with the pad. This can be caused by a dirty circuit board. 

Insufficient Wetting (Pin): If a solder in a joint has not wetted the pin at all and has only partially wetted the pad. In this case, heat was not applied to the pin and the solder was not given adequate time to flow.

Insufficient Wetting (Surface Mount): Assume that we have three pins of a surface mount component where the solder has not flowed onto the solder pad. We can heat the solder pad with the tip of the iron, then apply solder until it flows and melts together with the solder already on the pin.

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