Temperature Management In Selective Soldering

Temperature management is critical in selective soldering. The consequences of improperly managed temperatures is cracked boards, poor quality connections and – overall – more units of inferior product being caught by QC and worse, going out to customers. 

Obviously, turning out defective product is to be avoided whenever and wherever it can. One of the most common defects in PCBs are defects due to thermal shock. Cracked boards, melted components and so on are the warning signs, and unlike poor connections, often require the entire board to be scrapped instead of just touching up a connection. 

However, it takes more than just monitoring the temperature of the solder or the selective soldering machine. Here are some crucial aspects of temperature management to monitor to ensure against thermal shock. 

Soldering Component Preheating Is A Must

The most critical aspect, of course, is preheating. The board and components must be brought up to the proper temperature to ensure that thermal shock doesn’t occur. This is the single biggest culprit of boards cracking after they leave the soldering machine. 

Micro cracks in the board widen as a board that isn’t preheated to the correct temperature, resulting in larger cracks if not entire fractures. This results in a wasted board. That said, preheating is a known quantity for any operation that employs selective soldering. Careful selection of a selective soldering machine will ensure that your equipment includes preheating, ensuring that it isn’t a problem. 

Soldering Method Thermal Concerns

Another aspect of soldering that can result in thermal shock and damaged boards is the soldering method itself. After all, molten solder that is being applied to the board and components exposes both to a considerable amount of heat. Therefore, you’ll want to make sure that as little heat transfer as possible takes place, and therefore, you need to select the soldering method that accomplishes the solder joints you need while exposing your board and components to as little heat transfer as possible.

The least amount of heat transfer occurs with laser soldering as very little heat transfer occurs. If heat isn’t a huge problem, laser and selective soldering are both candidates to consider. Selective soldering, if appropriate, is the most effective middle ground between methods as some does occur, but only when and where soldering is required. However, the most amount of heat transfer occurs with wave soldering.

Therefore, you want to make sure to select the right soldering method for your company and for your product. Does this mean that every company should use laser soldering exclusively and never employ wave soldering again? Hardly; laser soldering is overkill when a company makes mass amounts of simple boards with surface mount components; a reflow oven is the better option. It’s more the case that you should make sure the selective soldering method you’re using the right one for you. 

Examine Solder Joints

Another area of temperature management is the solder joints themselves. This is an area which can be overlooked, but is of just as critical importance as the soldering method and preheating, as solder joints that melt components or crack the board are just as much an impairment. 

What you need to look for is excessive solder being applied to the joint. Obviously, too little solder will result in a poor connection that needs to be fixed later or requires a whole new board to be created. However, too much solder can result in excessive thermal stress being placed on the board. Since solder is a molten alloy, the more of it that a board and components is exposed to means a greater amount of heat that they are subjected to. 

The more and longer a board is subjected to excessive heat, the greater the odds become of thermal shock and a compromised product. Therefore, take care to examine each product as the soldering comes to a close.