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From the survey, there are many PCB explosions. This is one of the most common quality reliability defects. The causes are relatively complex and diverse. In the welding process of electronic products, the greater the probability of explosions when the welding temperature increases. .
The cause of the board burst is mainly due to insufficient heat resistance of the substrate, or some problems in the production process, such as high operating temperature or long heating time.
The main reasons for the explosion of the copper clad laminate are as follows:
Insufficient curing of substrate
Insufficient curing of the substrate reduces the heat resistance of the substrate, and the copper clad laminate is prone to bursting when the PCB is processed or subjected to thermal shock. The reason for the insufficient curing of the substrate may be the low heat preservation temperature of the lamination process and insufficient heat preservation time, or The amount of curing agent may be insufficient.
When the user responds to the failure of the board, you can first check and solve the failure method from the following aspects!
1. The substrate absorbs moisture
If the substrate is not well stored in the storage process, it will cause the substrate to absorb moisture, and the release of moisture during the PCB board process can also easily cause the board to burst. The PCB factory should repackage the unused copper clad laminate after opening the package to reduce the moisture absorption of the substrate.
For the pressing of multilayer printed circuit boards, after the prepreg is taken out of the cold base, it should be stabilized in the above air-conditioned environment for 24 hours before it can be cut and laminated with the inner layer. It takes one hour after the completion of the lamination The inside is sent to the press for pressing to prevent the prepreg from absorbing moisture due to dew point and other factors, causing white corners, bubbles, delamination, and thermal shock of the laminated product.
After being stacked and fed into the press, the air can be pumped first, and then the press can be closed, which is very good for reducing the impact of moisture on the product.
2. The substrate Tg is low
When using copper clad laminates with relatively low Tg to produce circuit boards with relatively high heat resistance requirements, because the heat resistance of the substrate is low, the problem of board bursting is prone to occur. When the substrate is insufficiently cured, the Tg of the substrate will also decrease, and the PCB The board production process is also prone to bursting or the color of the substrate becoming darker and yellow. This situation is often encountered on FR-4 products, and it is necessary to consider whether to use a copper clad laminate with a relatively high Tg.
In the early production of FR-4 products, only epoxy resin with Tg of 135°C was used. If the production process is not suitable (such as improper selection of curing agent, insufficient curing agent dosage, low insulation temperature during product lamination, or insufficient insulation time, etc.), the substrate Tg is often only about 130 degree Celsius. In order to meet the requirements of PCB users, the Tg of general-purpose epoxy resin can reach 140 degree Celsius. When users report that the PCB process has a problem with the board or the color of the substrate becomes darker and yellow, you can consider adopting a higher level Tg epoxy resin.
The above situation is often encountered in composite CEM-1 products. For example, the CEM-1 product has a burst in the PCB process, or the color of the substrate becomes darker and yellow, and "earthworm patterns" appear. This situation is not only related to CEM- 1 In addition to the heat resistance of the FR-4 adhesive sheet on the surface of the product, it is more related to the heat resistance of the resin formula of the paper core material. At this time, the resin formula of the paper core material of the CEM-1 product should be improved. Work hard on the heat resistance.
After years of research, the author has improved the resin formula of CEM-1 paper core material and improved its heat resistance, greatly improving the heat resistance of composite CEM-1 products, and completely solved the problem of wave soldering and reflow soldering. Time burst and discoloration issues.
3. The influence of the ink on the marking material
If the ink printed on the marking material is thicker and it is placed on the surface that is in contact with the copper foil, because the ink and the resin are incompatible, the adhesion of the copper foil may decrease and the problem of plate bursting may occur.
The problem of board explosion can be solved from the above three methods. The PCB board production process is basically automatic mechanization. It is inevitable that problems will occur during the production process. This requires us to strictly control the quality of people to make qualified PCBs. plate!
