For many engineers, designing electronics has become more about schematic capture, circuit simulation, and PCB layout than working with the actual hardware. It may be weeks or months before you pick up a soldering iron, and in some cases, new designers may be utterly unfamiliar with the skills necessary to create a good solder joint. This scenario often leads to mistakes, cold solder joints, burnt boards, intermittent circuit behavior, and frustration. Here, we’ll look at some of the problems to avoid during soldering and some of the best practice PCB soldering techniques that can help.
PCB Soldering Problems to Avoid
The poor soldering of its components can completely undermine a printed circuit board that has been flawlessly designed and perfectly built. Here are the three main areas you need to be aware of that can cause soldering problems on your PCB:
Oxidants and contaminants:
The soldering process is designed to break down minor amounts of contamination but can’t work through a thick layer of oxidants. The metal surfaces should be cleaned of visible contamination to ensure a good solder joint. It is also a good idea to clean the tip of your soldering iron to ensure that it is conducting the full amount of heat during soldering.
Applying heat:
Applying the right amount of heat during soldering is important to form a solid connection. Too little heat could cause damage to the pads and traces on the circuit board or the components, and the excessive heat can create collateral damage to nearby components.
The amount of solder:
The correct amount of solder must be used to create a good connection between the component leads and the PCB pads. Too little and the connection will be solder starved and weak, resulting in a broken joint. Too much and the excess solder could mask other problems or bridge to other undesirable connections.
To help people understand these problems and how to avoid them, IPC has developed standards for soldering components to circuit boards.
Standards for Soldering PCB Components
IPC-7711C/7721C details the steps necessary to rework, modify, and repair electronic assemblies. This standard covers soldering components and includes information on the following:
- Un-soldering and then soldering components back into a circuit board.
- Removing and replacing conformal coating to access components for rework.
- Repairing damaged holes needed for soldering.
- Delamination or blister repair.
- Bow and twist repair.
- Broken or lifted metal trace repair using jumper wires, sealers, and adhesives.
Circuit board manufacturers usually require their technicians to be well trained in these standards and the art of PCB rework techniques. Here are some of the basic PCB soldering techniques they use every day that can also help us.
PCB Soldering Techniques that Produce Good Results
To create better solder joints and avoid the problems outlined above, consider the following soldering recommendations as you work on your next project:
Equipment:
Your tools and materials, such as soldering irons, solder, etc., should be of good quality and comfortable to hold and use. You will also want to ensure that the soldering iron you use has sufficient heat for creating good strong solder joints.
Preparation:
Ensure that the surfaces to be soldered are free from oxidation and other contaminants before soldering them so as not to overwhelm the cleaning capabilities of the flux. Most oils or dust will wipe off, but you may need to use a chemical cleaner in some instances. Clean surfaces include your soldering equipment, so be sure to wipe the iron on a cleaning pad and tin the tip with the solder.
Soldering:
- Apply a little solder to the tip of the soldering iron to help it conduct heat during the soldering process.
- Hold the iron tip firmly against the board surface and component lead for enough time (a few seconds) to heat both simultaneously. However, be careful not to burn through to the board.
- Place the solder (which is usually a spool of “solder wire”) against the heated surfaces and the iron’s tip, and keep feeding the solder until enough has been added for a good joint.
- Remove the soldering iron and the solder, allowing the connection to cool without stress to form a good solid joint.
The goal:
- The solder should have completely melted and flowed for good adherence to the metal surfaces in a process called “wetting.”
- Surface mount parts: A concave solder filet should have been formed on the edge of the component leads sitting on a metal pad.
- Thru-hole parts: The solder should have filled the hole, creating a small tear-drop shape around the lead.
- The hardened solder joint should be shiny and clean.
Additional Soldering Recommendations
Like anything else in life, getting good at soldering connections on a PCB requires practice. If nothing else, take an old unusable circuit board and practice removing and reinstalling some components to sharpen your soldering skills. This practice will help you learn the proper amounts of time and heat to create a good solder joint without risking a new circuit board
Another alternative is to enlist the help of the PCB contract manufacturer that built your board in the first place. PCB CMs usually have a team of technicians that are IPC trained and certified for soldering already in place. If you need some components changed around during the prototyping phase of your design, get the CM involved. This type of work is what they do, and they have a lot of experience reworking circuit boards. Your PCB CM can also give you a lot of advice and help during the design phase of your board that will help you place parts and route connections on the board to avoid soldering problems.
At VSE, we have a highly trained staff with years of experience reworking circuit boards. We also have state-of-the-art production facilities, equipment, and materials that our manufacturing teams use while building our customer’s projects. VSE not only uses trained and experienced technicians on our production line, but we also employ certified IPC trainers that ensure our staff is at the top of their game when it comes to working on your printed circuit board.
