PCB warping can lead to costly consequences if it is not dealt with early. It is a problem that is very common and can cause serious problems for manufacturers, designers, and fabricators of PCBs around the world.
A printed circuit board that experiences warpage will lose its flat profile and curl at the ends. This can cause serious problems later on.
- Flat surfaces are best suited for pick-and-place machines. These machines can place parts incorrectly onto a PCB’s face if a board is warped.
- Wave solder machines are able to flood the board with solder when the curves inward. This acts as a basin, pooling the solder.
- The end product may not fit if the PCB board is warped. Even though the board may still be functional in theory, it can’t be scaled up.
These issues show that PCB warping can cause damage to a batch of manufactured boards and waste time and money. The reasons for PCB warping can be avoided before they happen. This blog will explain what causes PCB warping and the steps you can take to avoid it.
What Is PCB Warping?
Warping can cause printed circuit boards to become unusable. Due to their manufacturing process, all PCBs will experience some degree of warping. Any warpage below 0.75% is generally considered within industry specifications. However, this can vary depending on the product’s end use. Untrained eyes will not see this warping.
This movement must be accounted for in the layers of PCB boards. Multilayer printed circuit boards require that copper layers are balanced around the central layer. Equal weight distribution around the center reduces warpage.
To prevent warpage, it is possible to calculate the warp and weft for different prepregs. Preparations with different warp contents in the x or y directions have the potential to cause warpage. A board that has begun warping will warp more during soldering. This is due to heat activating the board’s locked-in stress.
Warping can also be caused by:
Heat sinks and PCB warping – Preheating is the most common cause of warping. However, it can also happen during soldering which uses localized heat to certain areas on the board. Warping doesn’t just occur at these stages. A PCB with heavy heat sinks can cause localized expansion and can lead to sagging during the transition phase.
Operating Temperatures – When printed circuit boards have been fabricated, they will go through intense heating and cooling. Fabricators need to be as efficient as possible in reducing the processing time and evenly heating each side of a board. Good fabricators will communicate with manufacturers to make sure they are familiar with warp and weft directions prior to lamination.
Fixing PCB Warpage
It is almost impossible to repair a printed circuit board that has become damaged. The best way to fix PCB warping is to mitigate the risks from the beginning through smart board design and understand the importance of thermal management in PCB manufacturing.
This section will discuss several methods that manufacturers and printed circuit board designers use to prevent or fix PCB warpage.
Designing Around Warpage
It is important to consider the possibility of warpage when designing printed circuit boards. All printed circuit boards will warp, but only if balanced designs are used. Design for manufacturability is an important aspect to consider to avoid these problems. There are a few ways you can do this:
- Balance layers on a multilayer printed circuit board so that the layer thicknesses are symmetrical in the middle of the printed Circuit Board.
- Prepregs and core sheets should be supplied by the same supplier to ensure that the coefficient of expansion is the same.
- To match the other side of a printed circuit board, match the outermost layers. Their thicknesses will differ if the copper areas are on opposite sides. This can cause warp.
Fixtures and Pallets
A pallet is used to clamp down PCB boards during manufacturing. This has been a traditional method for PCB makers. This method is familiar to those who have worked with watercolors. If you don’t tape down the sides of watercolor paints on paper, they will curl up. This is true for printed circuit boards that are placed in superheated environments. To prevent warpage, pin the corners and clamp the horizontal and vertical planes.
This method is not without its limitations. This fixture slows down PCB manufacturing, increases costs and decreases flexibility in high-mix environments.
Manufacturers have special machines that flatten boards that are not standard. These machines can only be used at specific points in the manufacturing process. Warpage after a PCB is completed is permanent. Some manufacturers use flattening methods, but the result is not always great and boards can rebound once they have been flattened.
Although tools are available for plate flattening, they are limited in their effectiveness. Proper PCB design is crucial for getting the best yield.
Addressing Environmental Factors
Proper storage can increase the risk of warpage. Copper clad laminates can absorb moisture, especially in high humidity environments. This risk can be reduced by using moisture-proof packaging. However, warehouse humidity can be controlled to prevent it from happening.
Also, if plating is pressed with heavy objects, it can cause warpage overall. It is important to monitor storage conditions in advance.
PCB warping is a major cause of delays and lower yields on printed circuit boards.& This is a problem for manufacturers. While PCB warping is most commonly caused by design, there are many other factors that can cause it. It is important to find a trusted expert in printed circuit boards to get the best results.
PCB warping is a common problem in the industry. However, with our experience and quick turnaround times, you can get the best value for your yield. For more information on our services, please contact us.
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