Causes Of PCB Warping & How To Prevent It

PCB Warping is among the most significant and complicated problems that can occur with printed circuit boards. It can also be an expensive problem if you do not identify it earlier. When the printed circuit board has a PCB warpage issue, it will no longer retain a flat profile and become curled at the end. This can inaccurately place the component on the face of a printed circuit board.

This issue can also give rise to other issues and cost you more. The best part is that the cause of the PCB warpage is easily identified, and you can prevent this issue by following some simple tips.

So, if you are also afraid of the PCB warpage issue and want to learn the cause behind this issue, you must read this article. It will highlight the significant cause behind PCB warping and give tips to prevent your printed circuit board from warping.

What causes PCB warping?

Generally, any warpage less than 0.75% is considered within industry specifications, though this may vary depending on the product’s end use. It’s hard for the average person to identify less warpage on these boards. Only trained eyes can find the PCB warpage issue. However, printed circuit boards, or PCBs, can only become useful if there is less PCB warpage. More warpage in printed circuit boards can make these boards unusable.

The presence of an imbalanced copper percentage in the different layers of printed circuit boards is the primary cause of PCB warping. The laminate of these layers comprises different types of material, like copper, resin, and more. These layers can also get locked-in stress when heated at extremely high temperatures, despite being flat. The thermal expansion causes movement under that stress. Thus, printed circuit boards require an account of this movement in a balanced manner.

When a printed circuit board or PCB begins to warp, it will continue to warp throughout the soldering process due to the introduction of heat, which activates the board’s locked-in stress. Apart from it, below is the other common cause behind the PCB warpage:

• Weight – Weight is also another common reason for the warping of printed circuit boards, as it can cause the board to deform and dent. Generally, the reflow furnace utilizes a chain to propel the circuit board forward, with the two sides acting as fulcrums to support the entire board. If there is a heavy part in the printed circuit board, it can give too much depression to the board and cause it to bend. 
• Heat sink – Heat sink is another major cause of warping printed circuit boards. It generally happens during the preheating and soldiering process, which involves applying localized heat to specific areas of the board. Heat sinks can cause localized expansion on the PCB or printed circuit board and can sag during the transition phase of the PCB boards. 
• Changing temperature – the printed circuit boards undergo intense cooling and heating during fabrication. This temperature change can also lead to warping of the printed circuit boards. Fabricators need to minimize the processing time of the fabrication, even while heating a printed circuit board.

Tips to prevent PCB warping

Fixing the PCB warpage is almost impossible; even trained professionals cannot fix this issue. The best way to fix this warping issue is to avoid mistakes while producing printed circuit boards. The following are the top tips that can help you prevent PCB warpage:

Designing 

True, all printed circuit boards warp to some extent during production, but the amount they warp depends on the balanced design. The best way to avoid a PCB warpage is to design a PCB or printed circuit board with the thought that it will warp. Below are the top ways to design printed circuit boards to prevent warpage:

• Matching the outermost coating or layers on both sides of a PCB or printed circuit board. If the thickness of the copper areas on both sides varies significantly, the warp will occur.
• Layer thicknesses on a multilayer PCB must be balanced so that they are symmetrical along the printed circuit board’s center.
• Using the same manufacturer for the prepreg and core sheet ensures the expansion coefficient is similar.

Bake the board before cutting.

Today, most printed circuit board manufacturers bake the board after cutting. However, using a baking board after the clad-cutting is a misconception for many manufacturers. But baking before cutting can also be an excellent option, as it can prevent warpage.

Prior to cutting the copper-clad laminate, the board is baked (150 degrees Celsius, 10 hours) to remove moisture while ultimately solidifying the resin and removing any remaining stress in the board, which helps prevent warping. 

Baking before or after cutting is feasible in both cases. It is advisable to make a decision based on the grade of the printed circuit board or PCB produced and the customer’s warpage requirements. But if you want to prevent PCB warping, you must prefer baking the printed circuit board before cutting. 

Straightened thin plate

The straightened thin plate is another easy method that you can follow to prevent warpage in printed circuit boards. If you do not straighten a thin plate, the sheet will bend after the electroplating of copper layers of 30 to 40 layers. 

Special clamping rollers should be made when using the 0.40.6mm ultra-thin multilayer board for surface and pattern electroplating. A circular stick clamps the entire flybus after a thin plate is loaded onto the flybus on the automatic electroplating line. The rollers are connected to straighten all the plates on the rollers, preventing distortion of the PCB after plating.

Use plates and fixtures.

PCB manufacturers have historically used a method of using plates and fixtures that clamp down the printed circuit board during its production process. You might be familiar with this method if you have used watercolor.

After applying a watercolor point, the sides will curl up themselves. This principle applies to superheated PCBs by securing the corners and avoiding warpage by clamping the vertical and horizontal planes. Unfortunately, this method can slow the overall production process, increase production costs, and reduce flexibility in a mixed environment.

Addressing the environmental factor.

Improper storage of printed circuit boards can enhance the risk of PCB warping. Copper-clad laminate can absorb moisture in certain weather conditions, especially in high humidity. Moisture-proof packaging can help reduce this risk. If you cannot find moisture-proof packaging, you can also minimize humidity in your warehouse. It can also help you reduce the risk of PCB warping.

Moreover, when heavy objects press the plating, it can also increase the risk of warpage of the printed circuit board. That is why monitoring the weather condition of storage is crucial. 

Conclusion 

PCB warping is among the significant issues affecting the overall performance of printed circuit boards. However, finding its cause and fixing it immediately is necessary to prevent expensive fixes. You can also follow the tips or tricks mentioned above to prevent printed circuit boards from warping.