Bridge soldering is a common thing that happens in PCB design. For printed circuit board designers, solder bridging is a mistake they always want to avoid. These designers always want their bridges to stay. But solder can be funny at times.
Bridge soldering or solder bridging is one of the issues designers face during SMT PCB manufacturing. This problem can be prevented. Circuit board designers can also prevent this problem from happening. In this article, we will be discussing what a solder bridge is, how to avoid it, and how to deal with it when it happens.
Bridge Soldering-What is it?
To have a perfect understanding of what bridge soldering is, you have to know what soldering is. Soldering is a way of bringing small pieces together on the surface of a circuit board. It connects electrical components on a PCB. Soldering is an important aspect of PCB manufacturing.
During soldering, materials such as soldering iron, soldering paste, and solder flux are used. The soldering process is simple and straightforward. However, mistakes occur. Therefore, bridge soldering is one of these mistakes.
Bridge soldering occurs when two or more component pads connect due to excessive use of solder. Normally, these pads are not meant to connect electrically on PCBs. This situation causes electrical shortages that can result in different kinds of havoc.
When a solder bridge occurs, it is difficult to identify. This is because it can have a microscopic size. However, it needs to be identified. Even the smallest solder bridge can cause serious havoc. Every component pin or pad is supposed to be separated from each other.
Bridge soldering connects these pads and creates a conductive path. Bridge soldering is often considered a microscopic situation that needs thorough guidance. Although solder bridge PCB can be repaired, it is better to avoid it.
Causes of Solder Bridging in SMT PCB
You must have been wondering what causes bridge soldering. Bridge soldering can happen in several stages of the circuit board manufacturing process. We already know how solder bridging occurs. Solder bridging occurs when;
- Excessive solder on surface mount pads are utilized due to incorrect specification of stencil
- There is a bad seal between a bare circuit board and seal during the process of printing
- Solder pads are bigger than that the gaps between pads
- Components placements are done imprecisely
- An inadequate amount of solder resist is used between pads
- There is insufficient solder paste volume
It is quite difficult to know the exact cause of this problem since several factors can cause it. Stencil thickness can also cause solder bridging. A thicker stencil will cause more paste on the pads. This may then make the paste overflow from one pad to the other. If there is any mistake in the process of solder paste printing, solder bridging might occur.
How to Prevent Bridging Solder
PCB designers can prevent solder bridging from occurring. It is better to prevent this mistake than to look for ways to correct it. Although PCB designers can’t control the assembly process, they can help to reduce the occurrence of this problem. Below are some measures that can help you to avoid solder bridging from occurring;
Utilize the appropriate pad diameter and hole size for through-hole parts
Solder bridging can be a result of extremely large holes or surface pads. A pad that is very large reduces the distance between the soldered surfaces. The reduction in the distance can cause Solder Bridge. It is, therefore, important to size the pad and plated it through hole correctly.
Apply solder mask properly
Improper application of solder masks can be another cause of solder bridging. A solder mask is used everywhere the solder is not wanted. During soldering, you apply a solder mask everywhere. It is important you apply it between the pins of the components. The risk of solder bridging can increase if the solder mask isn’t applied between the pins.
Utilize the appropriate lead lengths for through-hole parts
Solder bridges can result from through-hole components with very long leads. The appropriate lead length is determined by the size and thickness of your board. The type of soldering and the component size and mass will also determine the lead length.
Use a high-quality PCB assembly House
Employing the services of a contract manufacturer might help you with the risk of this problem. A contract manufacturer that will keep you informed about their process is a good one to work with. You can make an inquiry to know their processes better. Ask questions about how they carry out the inspection processes on the board and how they develop their stencils.
Put fiducial marks on your circuit board
When you put fiducial marks on your boards, it will enable a machine to identify your PCB and arrange all the placements on each part of your PCB. According to the IPC, three fiducials should be used. Two marks in opposite corners and one mark in another corner. Utilizing poor fiducials will increase the risk of solder bridging.
Design for producibility
It is important to design for producibility. This will help reduce the risk of bridge soldering. According to the Association Connection Electronic Industries, Level A is the suitable level for overall producibility. You can’t avoid small spacings in some designs; however, they can be avoided in many designs. Don’t use unnecessary small parts.
Cross check design rules for mask reliefs
An area on the circuit board layout that requires no solder mask application is a solder mask relief. Solder mask relief is a thin outline that surrounds surface mount pads, vias, and through hole pads. Before you create your design rules, it is advisable you create a relief that ranges from 0.00s inches to 0.008 inches for your surface mount components.
Avoid mixing new and old flux for solder paste
For solder paste preparation, it isn’t ideal to mix new and old flux. Mixing new and old flux during soldering can increase the risk of solder bridging. Adhering to these rules will go a long way in helping you prevent solder bridging.
How to Fix Solder Bridge
There are several reasons why solder bridging occurs. This includes incorrect use of solder masks, excessive solder, incorrect soldering technique. This defect can be avoided at times. However, there are times it happens. It is, therefore, important to learn how to fix this problem. To fix a solder bridge, you need a solder flask, solder wick, and temperature adjustable soldering iron. Follow these steps to fix a solder bridge.
- Monitor the temperature
Usually, you want a large tip to transfer sufficient heat into the solder wick. You need to monitor the temperature. Ensure the temperature is higher than the soldering temperature. This will compensate for the solder wick absorbing some heat from the joint.
For instance, if you solder at 270°C, you would have to increase the temperature to 300°C when utilizing the solder wick.
- Surface tension
Surface tension refers to the possibility of fluid surfaces to shrink into the smallest area possible. The type of skills you have got and how effective your flux is might help you to wick the bridge away without needing a solder wick. You can utilize surface tension.
Surface tension helps to remove the solder from the bridge. You can fix a solder bridge without utilizing a solder wick. You just need to clean the top of the soldering iron before you try again. However, you need to be careful, heating the pin or pad severely with this approach can damage the integrated circuit or PCB pad.
- Use the Solder wick
You will have to use some solder flux, put the solder wick above the bridge and use a soldering iron to heat carefully. The solder wick should absorb the solder. You will have to put some fresh solder wick as it becomes filled. Just a little pressure to transfer the heat is required.
The important thing here is to absorb the solder without overheating the circuit board or component. Immediately you remove the solder bridging defect, the solder left might be too little. You will need to apply more flux and put in fresh solder.
With these tips, you should be able to remove the solder bridge. Fixing solder bridges is something straightforward. So, you should be able to fix this defect in no time if you follow the tips discussed above.
Frequently Asked Questions
How do I solder printed circuit boards? There are steps to PCB soldering, these steps are;
- Iron preparation
- Surface preparation
- Components placement
- Application of heat
- Solder application to the joint
What does a bad solder joint mean? A bad solder joint is a joint that has insufficient solder. The insufficient solder makes the joint weak and increases the chances of failure and cracking. This defect can be resolved by reheating the joint and applying some more solder. This makes the joint strong enough.
What is a disturbed joint? A disturbed joint usually happens when there is a movement during the solidification of the alloy. The resulting joint looks frosted and shows a ripple pattern on the surface of the joint. This movement could be human or mechanical. You can solve this problem by reheating the joint and leaving it to properly cool.
Conclusion
Soldering is an important aspect of PCB manufacturing. Its importance can’t be underestimated. There are mistakes that occur in this process. However, one can take precautions by following some steps. Solder bridging is a common problem that can be prevented and fixed. The ability to detect and find solutions to this problem is important to ensure smooth PCB manufacturing.
