Causes of Solder Bridging and How to Reduce and Prevent It

With more compact and smaller electronic appliances now available and here to remain, one issue that manufacturers face increasingly is or involves solder bridging. From the name, it is a well-known defect, and this takes place when solder flows between the connectors. This causes a bridge. Now, with a circuit board having two points that shouldn’t be connected, connecting it with solder, this could cause an electrical short, and eventually lead to havoc.

In this article, we will be discussing what solder bridging is, the causes, and how to prevent it. Please read on, we have so much in stock for you.

What is Solder Bridging and Why is it a Problem?

A well-known SMT defect is regarded as solder bridging. This takes place when there is a flow of solder between the connectors leading to a short or “bridge”. When bridging occurs, most times, it isn’t obvious immediately. However, this can cause serious problems for the device or components of that device.

Furthermore, solder bridging can take place at many different parts during the process of manufacturing. At times, the solder paste print is the point whereby the squeezing of solder paste occurs between the stencil and PCB. This leads to the deposition of extra paste.

Another cause of this is problems relating to PCB fabrication, the reflow oven’s settings, a component’s placement pressure, and more. Also, excess solder can cause bridging. Excess solder between joints can cause solder bridges. No matter the cause of bridging, it is always an issue or a problem for the manufacturer.

What are the Causes of Solder Bridging

Note that bridging can easily happen at any stage during the process of PCB manufacturing. Below are some of the major causes of solder bridge:

  • A PCB that is poorly designed whereby the placing of large components are done on one side. This results to a problem whereby the weight distribution is unequal
  • No proper orientation for the components
  • Space between the component pads isn’t enough
  • The reflow oven’s setting
  • A component’s placement pressure, as well as different other causes

Solder Bridging Issues

Below are some well-known issues relating to solder bridging.

Tombstone

Tombstone has to do with a condition whereby a specific component is raised or lifted up when wave soldering, and then looks like a tombstone. Usually, the cause of this is due to having a lead length that is incorrect or making use of components having different requirements for solderability.

Too much solder

From the name, this happens due to too much buildup of solder. This has to do with fast conveyor belt as well as a wrong ratio between the lead length and the pad

Solder Balling

Solder balling results from when the solder attaches itself to the PCB when wave soldering is on. This can happen when there is too high temperature or the solder splashes back to the board.

Non wetting and dewetting

Non wetting has to do with solder leaving some exposed copper behind. This has to do with the fact that there’s a need for the changing of the flux or the components of the brass haven’t been well plated. For de-wetting, it has to do with molten solder covering a pad and then retreats leaving some solder behind. Molten solder refers to melted solder.

Lifted Pads

Now, this happens when there’s a need to remove the component and then leads to the lifting of the pad from the printed circuit board. Lifted pads occur due to a pad joint that is overworked or copper plating having an uneven layer.

Blow holes and pin holes

Both holes are caused due to much moisture present in the circuit board, as well as bad copper plating

Ways of Reducing Solder Bridging

Solder bridging occurs due to different issues, therefore there’s no specific way of getting rid of it. However, it can be prevented and stopped. We have taken our time to learn how to reduce solder bridging. We will be sharing some of these strategies for you to learn from.

Change the Design of the Printed Circuit Board

Looking closely at the design of the circuit boards could be a great step to reduce bridging. Some well-known areas to check include the adjusting of the aperture width. You can also check the area ratios. Most times, the addition of solder mask dams helps to arrest bridging.

However, this doesn’t always happen. Most times, contract manufacturers do not always know what to do when it comes to the optimization of the board design. However, when possible, it is a very effective way of reducing bridging, most especially by the adjustment of the aperture width as well as the area ratio.

Furthermore, you can add solder mask dams between the fine pitch pads in order to prevent bridging of the solder

Modification of the Reflow Profile

Speaking broadly, liquid solder usually flows toward a warmer surface. Therefore, if the leads are warmer compared to the pads, here is the place the solder moves to first. In order to alter this, this will work when there is an increase in the soak time. What this does is to equalize temperatures.

Also, when the time above the liquids is increased, it creates more flowing time for the solder to reach its intended destination. As soon as the leads and two pads get to the same or similar temperature, the solder wets both. This causes the movement of the solder to the right location

Normally, liquid solder first flows to the surface that is warmer. The leads of the component could be warmer compared to the pad as a result of their thermal mass which is lower, as well as an increase in air flow surrounding the lead. The increase in soak time equalizes different temperatures across this assembly; also, it reduces the solder’s tendency to flow into warm surfaces.

Reducing the possibility of off-contact solder paste printing

You can prevent this by changing the board design as well as the stencil. This ensures that off contact printing doesn’t happen.

To reduce the solder paste volume in these trouble areas, try to modify the stencil design. Another smart move is to change the design of the board. This gets rid of anything causing off contact printing.

Minimize the volume of the solder paste or component lead size

Solder bridge is a PCB defect that happens when solder gets to an area it shouldn’t be. You can also prevent solder bridging by minimizing the solder paste volume. Also, components with more lead can prevent the solder from flowing in between the leads. In addition, you can minimize bridging by performing stencil modification. This helps to minimize the location or solder paste volume on the solder mask defined pads.

Also, making use of a component with more leads will minimize the possibility for the solder to flow between the leads. You can increase the size of the component lead. This will help to absorb more solder volume. Hence, it prevents it from spilling between the pads.

Solder bridging issues could also occur when you design a pad for a long footed lead. However, you eventually use an alternative component with a shorter lead. Also, the solder has the most wet area on the pad. Thus, this leaves less volume of solder to flow up the lead.

Furthermore, thermal differences are challenging as regards gull wing leads. Solder paste may likely pool and result in bridges during reflow. Therefore, try and modify the stencil to minimize the volume of the paste printed on the land pad.

Solder mask application

The right application of a solder mask helps to minimize the risk of solder bridging. Also, the solder mask layer is an important layer of a PCB. The right application of solder resist can also reduce solder bridging. Solder resist is an ink that conceals the PCB surface.

Appropriate lead lengths

One of the causes of solder bridging issues is long leads with through-hole components. Therefore, what you need to do is to make use of the correct lead lengths based on the thickness and size of the circuit board. Also, the type of soldering will determine the lead lengths.

Fiducials

Precisely designed markers put into the PCB design can help to align the components on the circuit board. It is usually recommended to use three marks.  Poorly placed marks can result in improper alignment of parts. Therefore, this can result in solder bridges.

How To Prevent Solder Bridges

Solder bridge is a common problem that occurs in PCB fabrication. Sometimes, this problem can be inevitable. However, there are a few tips that can help you prevent the risk of solder bridging.  You can apply these tips in your circuit board design.

Utilize the right hole size and pad diameter for THT parts

Some solder bridges are caused by plated  holes and surface pads that are too big. Also, a large annular ring pad can reduce the distance between the surfaces of two adjacent pins. This reduced distance can increase the possibility of a solder bridge, particularly in a wave solder operation. Therefore, it is important to follow datasheets to use the right size for both the pad and the plated through hole.

Make use of accurate lead lengths for through-hole parts

Through-hole components having very long leads can result in solder bridges. It is important to always use accurate lead lengths. Also, the thickness and size of your board will determine the lead length for your application. The type of soldering and component size and mass will determine the correct lead lengths.  It is important to check out the lead length ahead of time. This will minimize your rework time. A good printed circuit board assembly house can be of great help.

Design the greatest producibility

It is important to design for producibility. This is applicable to both through-hole and surface-mount components. Also, it relates to the ease of producibility when the spacings and dimensions of land patterns are available.

The IPC sets some industry standards for PCB assembly and design. According to the IPC, Level A is the preferred level for general producibility. In many designs, small spacings are avoidable. However, they are unavoidable in some designs. The best thing is to avoid using unnecessary tight spacings or small parts.

Place fiducials on your circuit board

Fiducials are well designed markers PCB manufacturers put in circuit board design. They enable an automated machine to locate your PCB and align placement of each part on your PCB. Component placement is very easy when correctly done.

According to the IPC, three fiducial marks are necessary. Two marks should be in opposite corners while one mark should be in another corner. improper placement of fiducial marks can result in misplaced parts. Therefore, this can increase the risk of solder bridges. Also, avoid using poor fiducial marks.

Proper application of solder masking

Solder mask is a coating applied where solder isn’t needed. Also, the solder doesn’t adhere to the solder mask. It is important to apply a solder mask in important places, particularly between the pins of components. Failure to apply solder mask between pins inadvertently or on purpose. Therefore, this creates a high risk of solder bridging.

Work with a good PCB assembly house

You may not be able to monitor the manufacturing process as much as you would like. However, you can control who you work with. Most causes of solder bridging occur in the manufacturing process. Therefore, it is important to work with a manufacturer that prioritizes quality jobs. Employ a contract manufacturer that will walk you through the production process.

Also, you can ask questions to have a better understanding of their processes and procedures. You can inquire about the development of the solder paste stencils used. Also, you can ask about the PCB inspection processes they perform.

The steps mentioned above will help to prevent the risk of solder bridging in your PCB manufacturing. Therefore, it is important to follow these tips to avoid the risk of solder bridge. Soldering issues can have a negative impact on PCB’s functionality.

Conclusion

Solder bridge is a common defect in printed circuit boards. Most times, this problem occurs during the manufacturing process. However, understanding the cause of this problem can help to prevent it. As a PCB designer and assembler, you can prevent solder bridges from occurring. The best way to do this is to follow guidelines and tips that help to prevent it.