PCB Technical - Circuit board welding ink wrinkles and blisters

Circuit board welding ink wrinkles and blisters

The blistering of the circuit board surface is actually a problem of poor bonding force of the board, that is, the surface quality of the board, which contains two aspects:

1. The cleanliness of the board surface;

2. The problem of surface micro-roughness (or surface energy). The blistering problem on all circuit boards can be summarized as the above reasons. The bonding force between the coatings is poor or too low, and it is difficult to resist the coating stress, mechanical stress and thermal stress generated in the production process during the subsequent production process and assembly process, which will eventually cause different degrees of separation between the coatings.

Now some factors that may cause poor board quality in the production and processing process are summarized as follows:

1. The problem of substrate process processing: Especially for some thinner substrates (generally below 0.8mm), because of the poor rigidity of the substrate, it is not suitable to use a brushing machine to brush the plate. This may not be able to effectively remove the protective layer specially treated to prevent the oxidation of the copper foil on the board surface during the production and processing of the substrate. Although the layer is thin and the brush is easier to remove, it is difficult to use chemical treatment, so in the production process It is important to pay attention to control during processing, so as to avoid the problem of blistering on the board caused by poor bonding between the substrate copper foil and chemical copper; this kind of problem will also be blackened and browned when the thin inner layer is blackened. Poor, uneven color, partial black browning and other problems.

2. The phenomenon of poor surface treatment caused by oil stains or other liquids contaminated with dust during the machining (drilling, lamination, milling, etc.) process of the board surface.

3. Poor sinking copper brush plate: The pressure of the sinking copper front grinding plate is too large, causing the hole to be deformed, brushing out the hole copper foil rounded corners and even the hole leaking the base material, which will cause the sinking copper electroplating, spraying tin welding, etc. Foaming phenomenon at the orifice; even if the brush plate does not cause leakage of the substrate, the excessively heavy brush plate will increase the roughness of the orifice copper, so during the process of microetching and roughening, the copper foil at this place is very easy to cause excessive roughening., There will also be certain quality hidden dangers; therefore, it is necessary to strengthen the control of the brushing process, and the brushing process parameters can be adjusted to the best through the wear scar test and the water film test;

4. Water washing problem: The electroplating treatment of copper deposits has to go through a lot of chemical treatments. There are many chemical solvents such as acid, alkali, non-polar organic, etc., and the surface of the board is not clean with water. Especially the copper deposit adjustment degreasing agent will not only cause cross-contamination. At the same time, it will also cause poor partial treatment of the board surface or poor treatment effect, uneven defects, and cause some binding problems; therefore, it is necessary to strengthen the control of washing, mainly including the flow of washing water, water quality, and washing time, And the control of the dripping time of the panels; especially in winter, the temperature is lower, the washing effect will be greatly reduced, and more attention should be paid to the strong control of the washing;

5. Micro-etching in the pre-treatment of copper sinking and the pre-treatment of pattern plating: Excessive micro-etching will cause the orifice to leak the base material and cause blistering around the orifice; insufficient micro-etching will also cause insufficient bonding force and cause blistering. ; Therefore, it is necessary to strengthen the control of micro-etching; generally, the micro-etching depth of copper pretreatment is 1.5-2 microns, and the micro-etching before pattern electroplating is 0.3-1 microns. It is better to pass chemical analysis and simple if possible. The test weighing method controls the thickness of the micro-etching or the corrosion rate; under normal circumstances, the surface of the micro-etched board is bright, uniform pink, without reflection; if the color is uneven, or there is reflection, it means that there is a hidden quality risk in the pre-processing; note; Strengthen the inspection; in addition, the copper content of the micro-etching tank, the temperature of the bath, the load amount, and the content of the micro-etching agent are all items to be paid attention to;

6. Poor rework of sinking copper: Some sinking copper or reworked boards after pattern transfer may cause blistering on the board surface due to poor fading, improper rework methods or improper control of the micro-etching time during the rework process or other reasons; If copper plate rework is found to be bad on the line, it can be directly deoiled from the line after washing with water, then pickled and reworked directly without corrosion; it is best not to re-degrease or micro-etch; for plates that have already been thickened, they should be reworked. Now that the micro-etching tank is fading, pay attention to the time control. You can first use one or two plates to roughly calculate the fading time to ensure the fading effect; after the fading is completed, apply a set of soft brushes and lightly brushes after the brushing machine, and then press the normal production Process copper immersion, but the time of etching and micro-etching should be halved or adjusted if necessary;

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