Causes of deformation and warping during circuit board SMT patch processing

The IPC standard stipulates that the maximum allowable deformation of circuit boards for SMT patch processing is 0.75%, and the maximum allowable deformation of circuit boards without SMT patch processing is 1.5%. The circuit board warpage is calculated by: (PCB diagonal Long*2)*100%. Deformation and warpage of the circuit board will directly affect the welding quality, so SMT chip manufacturers are very troubled when encountering this problem. In order to meet the quality requirements of high-precision SMT chip processing, many SMT chip factories have very strict requirements on circuit board deformation and warpage. So what is the reason for the deformation and warping of circuit board SMT patch processing?

1. Analysis of the causes of deformation and warping during circuit board SMT patch processing

1. The V-cut on the circuit board is generally the main cause of deformation and warping. Because the V-Cut is to cut a groove on the original large sheet to obtain a small board, the V-Cut is prone to deformation. ;

2. Different circuit boards will have maximum heat resistance values. When the reflow soldering temperature is higher than the maximum value of the circuit board. It will cause the board to soften and cause deformation and warping.

3. After the general circuit board SMT patch processing is completed, it will be directly transported through the reflow soldering equipment track. If there are overweight parts on the board or the board is too large, and the reflow soldering temperature is high, the board will be dented in the middle due to its own weight and heat, causing bending and deformation.

4. Electronic products are developing in the direction of small size and lightweight, and the thickness of circuit boards is becoming thinner and thinner. Thinner circuit boards are more likely to deform at high temperatures.

5. Generally, a large area of copper foil is designed on the circuit board for grounding. When these large-area copper foils are not evenly distributed on the same circuit board, it will cause uneven heat absorption and heat dissipation speeds, and will also cause warping and deformation after cooling;

6. Since many incoming circuit board materials are not in their original packaging, due to environmental problems during storage, there will be more or less moisture in the circuit boards. If there is no baking operation before SMT patch processing of the circuit board, water will evaporate when the reflow soldering temperature reaches a high temperature, resulting in deformation and warpage;

2. Solutions to the deformation and warping of circuit board SMT patch processing

1. Most SMT chip factories use reflow soldering tracks to transport circuit boards. First of all, we try to use the long side of the PCB board as the contact point with the track, which can reduce the weight of the circuit board itself. This prevents the circuit board from deforming and warping.

2. If the above point 1 is not improved, the problem of deformation and warpage can also be solved by passing the pallet through the mesh belt of the reflow furnace;

3. If the circuit board is deformed during SMT patch processing and reflow soldering, a jig must be made to assist based on cost and production batch size.

4. If the circuit board is not in the original packaging, it needs to be baked at 120 degrees Celsius/about 4 hours before SMT chip processing to avoid deformation and warpage caused by the presence of moisture during reflow soldering;

5. Since V-Cut will destroy the structural strength of the PCB board between impositions, try not to use V-Cut daughter boards, or reduce the depth of V-Cut. Or give relevant departments improvement suggestions and propose using stamp holes to connect the impositions.

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