Common Selective Soldering Problems

Selective soldering is a very viable method of assembling components with through-hole technology, though it is not without issues. Any industrial process can have complications. 

Therefore, it behooves the manufacturer to know what problems can arise and how to deal with them. The following items are known selective soldering problems and their respective fixes. 

Excess Solder Such As Solder Bridges, Webbing and Solder Balls

One issue that can arise with selective soldering or indeed any method is excess solder. You’ll most often see it in the form of solder bridges – links between solder joints – webbing and small balls of solder deposited on circuit boards. This is a serious issue, as it means solder is adhering completely to the joint, which should be the only part of the board with solder on it. 

A common cause is insufficient nitrogen or impure nitrogen if soldering in a nitrogen-rich environment. Nitrogen is more stable than air, which creates better, more consistent solder joints. 

However, it is not the only known cause. Insufficient solder pot temperatures can mean the solder is already starting to solidify as it is applied. Dwell and drip times can also create excess solder issues if set too long. 

Additionally, using too weak a flux for the application can likewise create the issue. What happens in this instance is the flux doesn’t hold up to the soldering and creates excess. 

Check your nitrogen, and try adjusting dwell and drip times. Switching to a hardier flux can also help reduce this issue. 

Cracked Circuit Boards

Another common issue is circuit boards cracking during selective soldering. This can happen occasionally, as circuit boards (being a wafer-like material) are not the hardiest of objects. However, if you have chronic issues with cracked boards, then you likely have a temperature management problem

In this case, too much heat is present during the soldering process, making the boards more brittle and leading to them breaking. Supplier problems do occasionally arise as well, so don’t count it out. 

Among the more common culprits, however, is insufficient preheating. Boards should be tempered by preheating prior to soldering, so that thermal shock and subsequent breakage doesn’t occur. Try adjusting your preheat to see if that addresses the issue. 

If your process doesn’t call for preheating, baking the boards prior to soldering can also address the issue. 

Copper Pad Dissolution Or Lifting

Another common problem in selective soldering is dissolution of the copper pad where the component is inserted into the board. A related issue is fillet lifting, where the copper pad warps when solder is applied, creating a cone-like shape of the copper pad. 

Fillet and pad lifting are harder to prevent than some other selective soldering problems, as it may require a harder fix than merely switching flux or dialing up the preheat. Different boards may need to be sourced, as the copper pads may be too small for the joints being created. Reducing pad size and adjusting the soldering site can also be effective. 

Additionally, boards of poor quality can also experience more issues than higher quality boards. We all want to get lean and reduce costs. However, quality of product is not an area where you want to skimp. 

Copper pad dissolution occurs when the copper melts and becomes part of the solder solution. Lead-free solders are more susceptible to this phenomenon than leaden ones. To prevent it, apply thicker copper pads. You may also want to ensure that your solder has a copper content of 1 percent or more.