Guideline

Common Mistakes to Avoid in PCB Assembly and Manufacturing

Common Mistakes in PCBs

The Printed Circuit Board places various electronic components, such as chips, resistors, capacitors, etc., over its board. The PCB manufacturing and assembly process is a complicated procedure which consists of more than 50 steps and requires large investments in different equipment as well. The PCB manufacturers give due importance to the quality and consistency of PCB manufacturing processes, especially in launching new products.

This is because discovering defects during the PCB assembly and manufacturing process not only hinders the progress of the whole process but also leads to costly redesigning and testing cycles, increased warranty claims, and tarnished brand reputation once the final product reaches the customer. Therefore, the following is the list of common mistakes that one must avoid to reserve resources and prevent getting stuck in the loop of constantly redesigning and testing the same product.

Common Mistakes in PCB Assembly

1. Trapped Solutions

Some etching solutions are used to remove extra copper from the PCB board during the PCB board assembly manufacturing process. Sometimes, these solutions get trapped in the sharp regions on the board and result in corroding the traces, which ultimately defects them.
To avoid this mistake, it is better to look out for patterns attached at a 90-degree angle to the pad, which can help the user fix the regions where the solutions get trapped.

2. Test Point

During the designing stage of the PCB manufacturing and assembly process, it is a good move to add hooks so that it becomes easier to test crucial components. Test point is a place on the board where the test signals are inserted, and the circuitry is observed. Those who ignore such test points during the design stage are more likely to face component errors in the later stages which not only hinder the PCB assembly and manufacturing process but also lead to additional modifications and sometimes rework the design.

3. Visual Elements

All the essential information related to component outlines, reference names, first pin marks, etc. is embedded in the overlay layers which not only help the PCB assembly and manufacturing process but also aid post-manufacturing troubleshooting. To prevent layout discrepancies, it is advisable to ensure all the required information is correct and appropriately recorded.

4. Unsuitable Design

Most PCB board assembly manufacturing problems stem from issues in its design. Some common design-related issues include less spacing between traces, acute trace angles that are too sharp for manufacturing capabilities, fine spaces with less tolerance for the fabrication process to succeed, etc. Apart from these problems, other issues, such as narrow traces that allow damage from electrostatic discharge, symmetrical designs posing a risk of acid traps, thermal relief problems, etc., also occur. Many design-related problems can be avoided by undertaking rigorous design for manufacturability (DFM) analysis and thoroughly following PCB design guidelines. It is better to involve fabrication engineers in the design stage as they help assess design manufacturability. Moreover, simulation and modeling tools come in handy when a design’s tolerance to real-world problems and problematic areas have to be identified.

5. Risk of Contamination

During the PCB fabrication process, some substances such as flux residues, finger oils, cleaning agents’ residuals, and acidic plating solutions can lead to contamination which may cause problems, including electrical shorts, open circuits, corrosion, etc. Therefore, it is necessary to keep the production areas clean and take extra care while following handling procedures.

6. Defective Materials

The materials used in the PCB manufacturing and assembly must be free of defects and manufacturers must ensure that they are bought from reputable suppliers who do not compromise on quality. Low-quality materials can contain resin starvation, pinholes, nodules, etc., which may cause problems in the later stages.

7. Mechanical Failure

Since PCBs are composed of fragile and sensitive components, they are prone to mechanical failure. As the PCB board assembly manufacturing process involves many stages in which PCBs encounter different surface finishes and equipment, they often get scratches and dents. Such damage can be minimized by handling them carefully and proper techniques of PCB loading, moving, and storing are followed. Additionally, frequent inspection of boards between different stages helps catch the damage early.

8. Variations in Regular Processes

The variations in regular processes can result in PCB defects if important factors such as inaccurate or imprecise temperatures, non-target drill rates, uneven lamination, and inadequate storage facility occur, and things go beyond control limits. Therefore, to prevent such issues, statistical methods can be used to detect when such factors deviate from the tolerable limits. Control charts are also a great tool for tracking the factors and minimizing variability-related problems.

9. Soldering Defects

During the PCB manufacturing and assembly process, most defects originate when components are soldered improperly onto boards. Some common soldering issues include solder bridging (when two areas that need to be electrically isolated are soldered), voids (when small gaps remain within joints due to missing solder), cold solder joints (insufficient heat given during soldering results in joints that consist of incomplete wetting between different surfaces), and solder balls (balls that converts into small independent pieces), etc. Soldering is an important part of the process that must be carried out properly. Hence, strict protocols and inspection procedures must be followed extensively.

10. Defects in Dimensions

It is important to take care of PCBs’ dimensions since accurate dimensions are necessary for the PCBs to function properly. Common dimensional issues include skew (inner layers being shifted due to misalignment between different layers), incorrect pattern (layers are aligned incorrectly which leads to the holes to not line up in a specific pattern), incorrectly drilled holes (holes that are drilled in the positions other than their intended location), and overall intolerable spaces and traces that can result in short circuits. To prevent such issues, manufacturers must take care of the precision of dimensions and calculate them several times before finalizing them.

Common Mistakes in PCB Manufacturing

11. Plating Defects

The plating that is applied to PCBs must be of quality and free of any defects. Defects such as nodules (bumps that exist in the plated copper surface), pits (spaces and depressions in the plating surface), dull textured plating, and thinner plating than the required specifications can all lead to either poor connectivity or excessive soldering.

12. Drilling Defects

Drilling defects, such as smear (the residue of resin that is left around holes after drilling), improper holes (holes having imprecise diameter or imperfect circularity), rough hole edges, incorrect hole centers, etc., result in incorrect connections between layers. Therefore, not only the drilling must be done with complete precision and accuracy but also the dimensions of holes must first be calculated accurately as well.

13. Human-made Errors

Sometimes, humans can make mistakes that can damage PCBs. For instance, machine operators can integrate defects into PCBs while incorrectly loading boards into plating tanks, using drill bits of the wrong sizes, or inappropriately storing finished boards. All these mistakes can be prevented if adequate training programs, proper work instructions, redundant verification of machine setups, and increased automation are applied.

14. Insufficient Space between Edge and Trace

If the space between the edge and trace in the circuit layout is not kept optimum, the copper conductor placed outside can either get partially chopped or even cut at times. It can also lead to exposed copper and burrs surrounding the edges.

15. Mishandled Copper Slivers

During the printing stage of the process, some thin copper segments known as copper slivers are formed. In some cases, these slivers fall into the plating bath and deviate towards anywhere on the board which might result in a short circuit. Sometimes, these scattered copper slivers pose a threat to the board’s functionality in case of the removal of these photoresist slivers. Therefore, it is better to handle them with due care to protect the board.

16. Silkscreen Printing Errors

Silkscreen printing is the last step of the PCB manufacturing and assembly process. If it overlaps on the pad, PCB board, holes, etc., it can hinder the assembly process later on.

17. Buying Wrong Components

Sometimes wrong components are selected, which affects the assembly process. It is better to select standard components as they are available from various vendors. The customized parts can be bought from only a handful of vendors. Therefore, they do not prove feasible for mass production of PCBs and increase the cost at large.

Conclusion

In conclusion, the PCB manufacturing and assembly process is highly extensive and thorough and requires complete attention to detail. However, since it involves numerous steps and several components, making errors and causing defects to PCBs often becomes inevitable. Nevertheless, manufacturers should follow all the required safety measures and carry out the procedures according to the set standards to the best of their ability.

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