In the entire production process of PCBs, there are numerous critical control points. Even a small mistake can result in board breakage, and quality issues can be endless, which is a major concern. This is because even one faulty component can render most devices unusable.
Beyond these issues, there are also several hidden risks that can affect the reliability and performance of the boards. The author has compiled a list of the top ten problems commonly encountered. Here are some of the insights and experiences gained from dealing with them, shared for your reference:
1. **Layer Delamination**
Layer delamination is one of the most challenging issues in PCB manufacturing. Possible causes include improper packaging or storage leading to moisture absorption, excessive storage time beyond shelf life, material or process issues from suppliers, and poor copper distribution in design. Moisture is a common issue, and even with proper packaging, it's difficult to fully control during transportation and temporary storage. Once moisture is detected, using vacuum-sealed bags or aluminum foil bags along with humidity indicator cards can help. If the humidity level is too high, pre-baking at 120°C for 4 hours can often resolve the problem. However, if the issue stems from supplier materials or processes—such as brown (black) spots, PP dampness, insufficient adhesive, or abnormal pressure—the risk of scrapping becomes higher. To mitigate this, PCB suppliers should focus on process management and reliability testing, such as thermal stress tests, where a reliable factory should pass more than five cycles without delamination. Design-wise, choosing a Tg value above 145°C is safer, especially in lead-free environments. Large copper areas and densely packed buried holes should also be avoided to reduce delamination risks.
2. **Poor Solderability**
Solderability is another serious issue, particularly when it occurs in batches. Common causes include contamination, oxidation, black nickel, abnormal nickel thickness, solder resist shadowing, long storage, moisture absorption, and thick solder mask on pads. While pollution and moisture issues can often be resolved, other problems like black nickel or solder mask defects are harder to detect through incoming inspection. It’s essential to ensure the PCB factory maintains good process control, including regular analysis of gold plating solutions, stable concentrations, and internal soldering tests. For pad repair, clear guidelines must be set to avoid repairing BGA or QFP areas, which are prone to failure.
3. **Board Warping**
Board warping can occur due to poor supplier selection, abnormal production processes, inadequate handling of heavy work, improper transportation, or design flaws such as uneven copper areas. Design reviews should identify and avoid such issues early. Some thin boards may require wood pulp boards during packaging to prevent deformation, and clamps can be used to prevent over-bending.
4. **Scratches and Exposed Copper**
Scratches and exposed copper are signs of weak management and execution in PCB factories. While not always severe, they raise quality concerns. Many factories claim these issues are hard to fix, but improvements are possible with strong leadership and consistent pressure. Factories that prioritize scratch reduction have seen significant improvements in DPPM (Defective Parts Per Million).
5. **Impedance Issues**
Impedance is crucial for RF performance on mobile phone boards. A common problem is large impedance variations between batches. Impedance test strips are usually placed on the edge of the board, so suppliers should provide test reports and compare the edge and board diameters for consistency.
6. **BGA Solder Void**
BGA solder voids can cause chip malfunction and are difficult to detect during testing. High-temperature vaporization or impurities in the holes can contribute to this. Many HDI boards now use electroplated or semi-filled holes to prevent such issues. X-ray inspection after assembly is also recommended.
7. **Solder Mask Blistering or Peeling**
This is often caused by poor control of the solder mask process, using low-quality ink, or excessive heat during reflow. PCB suppliers should implement reliability tests and process controls to prevent batch failures.
8. **Poor Plugging**
Poor hole plugging leads to incomplete filling, exposed copper, and potential short circuits. These issues can be identified visually and addressed through incoming inspection.
9. **Poor Dimensional Accuracy**
Shrinkage during manufacturing and adjustments in drilling or CNC programs can lead to dimensional inaccuracies. Selecting a reliable supplier with strong process control is essential.
10. **Cavalier Effect**
Also known as galvanic corrosion, this occurs in OSP (Organic Solderability Preservative) processes where gold and copper interact. It causes copper pads to shrink, affecting component placement and reliability. Experienced manufacturers use software to screen affected areas and apply design compensations to minimize the risk.
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