Why Does the PCB Break?

PCB break refers to the phenomenons of copper foil blistering, substrate blistering and delamination due to heat or mechanical action during the processing of PCB; or when the PCB finished board is subjected to thermal shock such as dip soldering, wave soldering or reflow soldering, the phenomenons of copper foil blistering, substrate blistering, circuit separation and delamination are collectively referred to as PCB break.

The main reasons for copper-clad laminate PCB break are as follows:

The heat resistance of substrate is poor, or there are some problems of production processes. For example, the operating temperature is too high or the heating time is too long, etc. When the substrate is insufficiently cured, the heat resistance is also lowered, and when the copper clad PCB is processed or subjected to thermal shock, the break is likely to occur. The reasons may be that the holding temperature is low during the lamination process, the holding time is insufficient, and the amount of the curing agent may be insufficient.

When a PCB break occurs, we can check it from the following aspect!

1. Substrate moisture absorption

If the substrate is not well stored during the storage process, it will cause the substrate to absorb moisture, and the moisture release during the PCB process will easily cause the PCB break. The PCB factory should repack the unspent CCL to reduce the moisture absorption of the substrate.

For multi-layer PCB pressing, after the prepreg taken out from cold base, it should be stabilized in the above air-conditioned environment for 24 hours before being cut and overlapped with the inner layer. After the lamination is completed, it should be fed into the press within one hour for pressing to prevent the prepreg from abosorbing moisture due to dew point and other factors, resulting in quality problems in the laminate product, such as white corners, bubbles, delamination, and PCB will break when thermal shock. After the prepreg is pressed and fed into the press, the pump can be pumped first and then the press is closed, which is beneficial for reducing the influence of moisture on the product.

2. Substrate TG is lower

When a copper clad board having a relatively low TG is used to produce a PCB having a relatively high heat resistance requirement, if the heat resistance of the substrate is low, the problem of PCB break is likely to occur. When the substrate is insufficiently cured, the TG of the substrate is also lowered, and the problem of the explosion is likely to occur during the production process of the PCB or the color of the substrate becomes dark and yellow. This is often the case with FR-4 products, so it is necessary to consider whether to use a copper foil with a higher TG. In the early production of FR-4 products, only TG was 135 °C epoxy resin. If the production process is not suitable, for example, improper selection of curing agent, insufficient amount of curing agent, low holding temperature of the product lamination process or insufficient holding time, the substrate TG is usually only about 130 °C. For meet the needs of PCB users, the TG of general-purpose epoxy resins can now reach 140 °C. When the user reports a PCB break problem in the PCB process or the substrate becomes darker and yellower, a higher level of TG epoxy can be considered.

The above situation is also often encountered in composite CEM-1 products. For example, CEM-1 products can damage the angle in the PCB process, or the color of the substrate may become darker and yellower, and there are cases such as “earthworm stripe”. In addition to the heat resistance of the surface layer FR-4 adhesive sheet of the CEM-1 product, this is more related to the heat resistance of the resin formulation of the paper core material. At this time, we should work hard to improve the heat resistance of the resin formulation of the CEM-1 product paper core material. After years of research, when the resin formulation of CEM-1 paper core material is improved and the heat resistance is improved, the heat resistance of the composite CEM-1 product is greatly improved. It completely solves the problems of PCB break and discoloration during wave soldering and reflow soldering.

3. Effect of solder mask on marking material

If the solder mask mark of the marking material placed on the contact surface with the copper foil is thicker, since the solder is incompatible with the resin, the adhesion of the copper foil may be lowered and the problem of PCB break is prone to occur.

The PCB board production process is basically automatic mechanization, and small problems will inevitably occur during the production process. However, once the PCB explodes, it will be scrapped, so this requires our artificial strict quality control to make a qualified PCB board!