The Top 3 PCB Layout Tips and Tricks to Reduce the Pain of Rework After Assembly

This last holiday season, I put our Christmas tree into the stand, filled it with water, and decorated it as I usually do. But this time, there was a surprise waiting for me—the plastic stand had developed some cracks, and water was leaking out onto the floor. I tried to fix it with tape, glue, and even a rubber sealing compound. None of those remedies worked, however, and it was time for a replacement. The problem was, a fully decorated Christmas tree is not so easily moved from one stand into another.

This conundrum of how to rework my tree stand was oddly familiar to me in light of the rework problems I’ve faced on printed circuit boards. How your PCB components are placed and routed can have a large influence on how difficult any rework will be after the board is assembled. In fact, we have three big PCB layout tips and tricks we often recommend to our clients to help ease the rework process:

1. Send us a correct bill of materials (BOM).
2. Follow adequate design for manufacturing (DFM) guidelines.
3. Leave room for rework.

Here is a closer look at some of the common PCB rework problems that can be encountered, and how these big three tips and tricks can help ease some of that pain.

What Are Some of the PCB Rework Problems You May Encounter?

Having to perform rework on a printed circuit board takes time, and time usually translates to added expense. Although some rework is to be expected, excessive amounts of rework due to problems that could have been avoided will increase these expenses.

Additionally, printed circuit boards that aren’t designed to support potential rework could create even more pain by making the job more difficult. Here are some of the problems associated with rework you may encounter:

• Replacing parts: The fact that rework must be done at all unfortunate. When it is required because the wrong part was initially specified, however, it is an expense in time and money that shouldn’t have happened.
• Assembly defects: Another major cause of rework is having to repair parts that have not soldered correctly during assembly. When the soldering problems are due to improper DFM clearances in the component placement or incorrect component locations and rotations, it is again a painful waste of resources that could have been avoided.
• Inaccessible parts: In some cases, reworking components on the board is complicated by their proximity to other components. When they are too close or even hidden by other parts, it can make trying to work with them very difficult.
• No room for tools: Even if a part is accessible, rework can still be difficult if the part isn’t positioned so that tools, such as soldering irons, can reach them. For example, there isn’t room for a soldering iron to reach small parts like 0805 passive components if they are between two tall components, such as tantalum capacitors or connectors.
• Collateral damage: Parts that are placed too close to components that require rework, such as the resistors and capacitors that support a large ball grid array (BGA), may suffer damage from the rework of the BGA. This damage could be due to the heat of a soldering iron that came too close to them, or physical damage from tools or the technician. Now the victims of this collateral damage will also have to be reworked.

Excessive rework and the problems that are often associated with it can cause a lot of pain when trying to get your circuit boards built on time and under budget. Fortunately, some good PCB design practices can help to reduce the amount and difficulty of rework.

3 PCB Layout Tips and Tricks to Avoid Painful Rework Problems

It is not uncommon for there to be a small amount of rework during PCB manufacturing. You can greatly reduce the amount of any potential rework, however—as well as help to make the task easier—by following these good design practices:

• Provide a correct BOM: When the wrong parts are assembled to the board, it is usually because the wrong parts are specified in the build documentation, such as the BOM report. This can happen when the schematic isn’t synchronized with the layout, or part information in the design hasn’t been updated. By making sure that your BOM is 100% in sync with your PCB design, you will avoid the problem of having to rework incorrect parts.
• Follow DFM guidelines: Parts that don’t have the required spacing or are placed in the wrong locations or with the wrong rotations may cause problems during assembly. They may not be able to be automatically installed, or they may not solder correctly. In either case, rework will be required to correct these problems. You can greatly reduce the potential for this rework, however, by obeying the DFM requirements of your contract manufacturer.
• Allow room to rework: Problems during rework, such as inaccessible parts or insufficient room for tools, is due to how the components are placed on the board. The performance of the board is the primary concern, of course, and sometimes components must be placed tightly together for signal integrity or other performance factors. However, when those requirements aren’t as strict, it will be to your benefit to loosen up the component placement to allow more room for rework.

The best resource that you can go to for DFM rules and rework guidelines is the PCB contract manufacturer that will be building your board. They should have the information you need to make the design right and should be able to offer other tips and recommendations as well.

What Your Contract Manufacturer Wants You to Know About PCB Rework

Your PCB designer must consider how to make the job of rework easier because as the complexity and density of a printed circuit board increases, so does the potential for rework. Even with the best component placement layouts, assembly defects will still occasionally occur, and your PCB contract manufacturer will need the room to perform the rework.

Along with designing for potential rework situations though, it is just as important to plan ahead in your design for additional debug capabilities. There may be some circuits that will require more testing than others. There may also be sensitive components that need to be verified that are not covered in the planned testing due to accessibility or being in a developmental stage. In these cases, you will want to allow the same room for access as you would for rework, and you may even need to consider additional vias for probing or header pins for test access.

Here is where an experienced PCB contract manufacturer can really help. When you work with a skilled assembler, they should identify areas of the board that will need more room for potential rework or additional testing. They should also have the engineering expertise to aid in developing your board for rework and debug access, as well as manufacturing technicians that are highly skilled in their rework abilities.