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How Is Warpage Formed?
SMT is also called surface mount technology. In the case of heating, the PCB pads are combined with surface-mounted components through solder paste. This process is called reflow soldering. The circuit board is prone to warpage when it undergoes reflow soldering. For the factory, the first thing to do is to prevent the printed circuit board from warping during processing.
Cause of Warpage
In the production process of circuit boards, materials such as copper foil, resin, and glass cloth need to be pressed together. Because the physical and chemical properties of each material are different, the residual thermal stress generated during the pressing process will cause the circuit board to deform and cause the board to bend and warp.
Some special products or circuit boards customized by enterprises will have some irregular board shapes, but the interface devices should be placed in narrow places. It is easy to cause warping of the circuit board.
During the design process, the layout is unreasonable, resulting in a relatively large deviation of the copper foil distribution, and the copper foil is an important heat absorption and heat dissipation point, and the large distribution deviation will cause uneven stress on the circuit board and deformation. If the temperature is very high and reaches the Tg value of the material, the circuit board will cause softening or deformation.
How to Better Prevent PCB Warpage Problems?
- Increase Board Tension
When the length of the board exceeds 80mm, there is no copper in the board, and the board thickness is less than 1.0mm, which is easy to cause warpage (FR4).
- Reduce the Effect of Temperature on the Board
You can choose to lower the temperature of the reflow oven, which can reduce the occurrence of PCB board warpage, but there may be side effects, such as a short circuit of solder.
- Reduce the Size of the Board and the Number of Puzzle Pieces
Reducing the concave deformation caused by the weight of the circuit board itself can also reduce the number of panels. The principle is the same, reducing the weight of the circuit board itself to prevent deformation and depression.
- The Circuit Board Material Adopts High Tg Material
Tg is the glass transition temperature, that is, the temperature at which the material changes from glass to rubber. The lower the Tg value of the material, the faster it starts to soften after entering the reflow furnace, and the time it takes to become soft rubber will be longer. The longer it is, the more serious the deformation of the board will be. The use of high Tg sheet can increase the bearing capacity, and the price of the material is also more expensive.
PCB Treatment of Warped Boards
The standard factory will conduct a flatness check during the final inspection. Unqualified boards will be picked out, put in an oven, baked at 150 degrees and under heavy pressure for 3-6 hours, and cooled naturally under heavy pressure. Then remove the pressure and take out the board, and do a flatness check, which can save some circuit boards, and some boards need to repeat the process. There are some serious circuit boards that have not reached the standard after several processes, and can only be treated in an environmentally friendly manner.
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