Analysis of the Causes of Wrinkling and Foaming of Circuit Board Soldering Inks

Publish Time: January 05,2019

The blistering of the circuit board surface is actually a problem of poor board surface bonding, that is, the surface quality of the board surface. This includes two aspects:

1. The problem of cleanliness of the board;

2. The problem of surface micro-roughness (or surface energy). The problem of surface blistering 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 plating stress, mechanical stress, and thermal stress generated during the production process during the subsequent production process and assembly process, which eventually results in different degrees of separation between the plating layers.

Some factors that may cause poor surface quality during the production process are summarized as follows:

1. Problems of substrate processing: Especially for some thinner substrates (generally below 0.8mm), because the substrates have poor rigidity, it is not suitable to use a brushing machine to brush the boards. In this way, the protective layer specially treated to prevent oxidation of the copper on the surface of the substrate during the production process of the substrate may not be effectively removed. Although the layer is thin and the brush plate is easy to remove, it is more difficult to use chemical treatment. It is important to control the processing, so as not to cause the problem of blistering on the surface caused by the poor bonding force between the copper foil on the surface of the substrate and the chemical copper; this problem also occurs when the thin inner layer is blackened. Defects, color unevenness, partial black browning, etc.

The surface of the board during machining (drilling, laminating, milling, etc.) caused by oil or other liquid contamination and dust contamination of the surface is not good.

3. Defective copper brush plate: Excessive pressure on the front grinding plate of the copper sink causes deformation of the orifice, brushes out the copper foil fillet of the orifice, and even leaks the substrate, which will cause the process of electroplated tinned soldering Orifice blistering; even if the brush plate does not cause leakage of the substrate, an excessively heavy brush plate will increase the roughness of the copper at the orifice. Therefore, the copper foil is likely to produce excessive roughening during the micro-etching roughening process. There will also be a certain quality hazard; therefore, attention should be paid to strengthening the control of the brush plate process. The process parameters of the brush plate can be adjusted to the best through the wear scar test and the water film test;

4. Washing problems: Electroplating of copper must undergo a large number of chemical treatments. Various types of acids, alkalis, organic solvents, and other chemicals have many solvents, and the surface of the board cannot be washed with water. Especially, the adjustment of degreasing agents for copper will not only cause cross-contamination. At the same time, it will also cause the local surface to be poorly treated or the treatment effect is not good, uneven defects, causing some problems in the binding force; therefore, we must pay attention to strengthening the control of washing, mainly including the washing water flow, water quality, and washing time , And the drip time control of the board; especially in winter, when the temperature is low, the washing effect will be greatly reduced, and more attention should be paid to the control of the washing;

5. Micro-etching in pre-copper pretreatment and pattern plating pre-treatment: Excessive micro-etching will cause the orifice to leak the substrate 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 depth of micro-etching before copper deposition is 1.5-2 micrometers, and the micro-etching of pattern electroplating is 0.3--1 micrometers. It is best to pass chemical analysis and simple conditions. The test weighing method controls the thickness or rate of micro-etching. Generally, the surface of the plate after micro-etching is bright, uniform pink, and no reflection; if the color is uneven, or there is reflection, it indicates that there is a quality hazard in the pre-processing process; note Strengthen the inspection; in addition, the copper content of the micro-etching tank, the temperature of the bath liquid, the loading amount, and the content of the micro-etching agent are all items to pay attention to;

6. Poor rework of immersed copper: Some reworked boards after immersed copper or graphics are re-processed because of poor faded plating, incorrect rework methods or improper micro-etching time control during rework, or other reasons will cause the board surface to blister; Rework of copper plate If the copper deposit is found to be bad on the line, it can be removed directly from the line after washing with water. Pickling can be reworked without corrosion; it is best not to degrease again and slightly corrode. Now the micro-etching tank is fading, pay attention to time control, you can 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 then lightly brush the board and then normal production Process copper, but the etch time is halved or necessary adjustments made;