DfRwk cannot be found in the list of DfX Design Guidelines. DfX refers to various design guidelines collected under the heading “Excellent Design”. You may have heard of more popular guidelines, such as design for manufacturability (DFM), design for assembly (DFA), or design for test (DFT). But what about design rework (DFRWK)? DFRWK is not yet part of the guide series, but it should be.
The meaning of rework PCB
Rework refers to any operation that needs to be completed after the main printed circuit board assembly operation is completed. Rework tasks are generally divided into two categories:
Problems in the design must be resolved, such as: the schematic symbol is inconsistent with the PCB package (which may cause the signal to be sent to the wrong pin); the wrong resistance value is selected; the wrong IC is selected; and the operation between the two pins is forgotten The necessary connections (and jumpers need to be added).
The design must be changed for specific reasons, such as: new functions need to be created; specifications need to be changed; components need to be switched.
In the former case, an error occurred during the design or assembly process, so it is necessary to change the components or PCB traces for repair. In the latter case, the expected design can work, but it turns out that it is no longer required for the product, so the components or PCB traces need to be changed to adjust the design. PCBA rework mainly involves heat and solder, but it may also require mechanical operations such as cutting traces or modifying physical components. When designing a printed circuit board, you may not often consider (if any) how your design choices affect future rework operations. But during prototype board development, testing, or deployment, rework is often necessary.
PCB rework and PCB repair
You may be studying the above situation and think that the “fixed problem” in PCB is the same as PCB repair. The difference comes from where the error occurred. When the circuit board fails for some specific reasons, it is usually repaired. There may be an ESD strike or reverse polarity connection. This means that repairs are necessary because someone may have discarded the PCB due to an unexpected failure. On the other hand, rework means that there are design errors that need to be corrected.
6 tips for rework PCB
Having defined the meaning of rework on PCB, let us understand how it is done! You can now take the following six steps to improve the design of DFRWK.
Make the PCB bigger
The prototype rarely needs to be as small as the final design, so please enlarge the prototype PCB and place it in a ready-made prototype enclosure. This will allow you to publish your design faster and waste less time dealing with tricky PCB layout issues. To test as part of the system, use cables to connect the larger prototype PCB to a tight location in the system. Larger PCBs are easier to work on the workbench, easier to detect, and easier to rework.
Use larger components
Although using tiny BGA components or 01005 package resistors may look cool and avant-garde, you may not need them and you definitely don’t need them on the prototype. You can’t easily rework parts smaller than a sugar. For prototypes, unless absolutely necessary, consider using parts no smaller than 0402, and use parts with exposed leads instead of BGA or QFN packages if possible.
In the μModule product guide, LinearTech reminds us how ugly rework is. (This is what happens when rework is not designed)
Allow more clearance
When there are more gaps around the part, rework is easier and more reliable. For BGA, QFN, or other packages without exposed leads, allowing enough space around it is essential for partial rework reflow heating. For high-density connectors or press-fit connectors, tools using PCBs require clearance. For mechanical parts such as radiator snap-in pins, the clearance of hand tools such as pliers is important