These are the reasons for the blistering of the copper plating surface of the circuit board

2021-09-13

Author：Aure

Board surface blistering is one of the more common quality defects in the circuit board production process, because the complexity of the circuit board production process and the complexity of the process maintenance, especially in the chemical wet treatment, make the prevention of the board surface blistering defect comparison difficulty. Based on many years of actual production experience and service experience, the author now makes a brief analysis of the cause of blistering on the surface of the copper plating of the circuit board, hoping to help the industry colleagues!

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

1. The cleanliness of the board surface;

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

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

The problem of substrate processing; especially for some thinner substrates (generally less than 0.8mm), because the rigidity of the substrate is poor, it is not suitable to use the brushing machine to brush the plate, which may not be able to effectively remove the substrate during the production and processing process. The protective layer specially treated to prevent the oxidation of the copper foil on the board surface. Although the layer is thin and easy to remove by brushing, it is difficult to use chemical treatment. Therefore, it is important to pay attention to control in the production and processing to avoid causing the board surface substrate. The problem of blistering on the board surface caused by the poor bonding force between copper foil and chemical copper; this problem will also cause poor blackening and browning when the thin inner layer is blackened, uneven color, and partial blackening and browning. First class question

These are the reasons for the blistering of the copper plating surface of the circuit board

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

Poor sinking copper brush plate: The pressure of the sinking copper front grinding plate is too large, causing the orifice to be deformed, brushing out the copper foil rounded corners of the orifice or even leaking the base material, so that the hole will be caused during the process of electroplating, spraying and soldering of the sinking copper. Foaming phenomenon; 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 micro-etching and roughening, the copper foil at this place is likely to be over-roughened. There will be certain quality hidden dangers; therefore, attention should be paid to strengthening 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;

Washing problem: Because the electroplating treatment of heavy copper requires a lot of chemical treatment, there are many chemical solvents such as acid, alkali, non-polar organic and so on. It will also cause poor local treatment of the board surface or poor treatment effect, uneven defects, and cause some bonding problems; therefore, it is necessary to strengthen the control of washing, mainly including the flow of washing water, water quality, washing time, and Control of the dripping time of the panels; especially in winter when the temperature is low, the washing effect will be greatly reduced, and more attention should be paid to the strong control of the washing;

The micro-etching in the pre-treatment of copper sinking and the pre-treatment of pattern electroplating; 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 depth of micro-etching before copper sinking 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 tests if possible. The heavy method controls the thickness of the micro-etching or the corrosion rate; in general, the color of the surface after the micro-etching is bright, uniform pink, without reflection; if the color is uneven, or there is reflection, it means that there is a hidden quality problem in the pre-processing of the process; pay attention to strengthen the inspection ; In addition, the copper content of the micro-etching tank, the temperature of the bath, the load, the content of the micro-etching agent, etc. are all items to be paid attention to;

The activity of the copper sinking liquid is too strong; the newly opened tank of the copper sinking liquid or the content of the three components in the bath is too high, especially the high copper content, will cause the bath liquid to be too active, the chemical copper deposition is rough, hydrogen, and cuprous oxidation The defects of the physical quality of the coating and the poor bonding caused by the excessive inclusion of substances in the chemical copper layer; the following methods can be appropriately adopted: reduce the copper content, (add pure water to the bath), including three components, Properly increase the content of complexing agent and stabilizer, and appropriately reduce the temperature of the bath liquid, etc.;

The surface of the board is oxidized during the production process; if the copper sink is oxidized in the air, it may not only cause no copper in the hole, the surface of the board is rough, but also may cause the surface of the board to bubbling; the copper sink may be stored in acid for too long, The board surface will also be oxidized, and this oxide film is difficult to remove; therefore, the copper sinking plate should be thickened in time during the production process, and it should not be stored for too long. Generally, the thickened copper plating should be completed within 12 hours at the latest;

Improper rework of the heavy copper; some heavy copper or reworked boards after the pattern transfer are poorly plated during the rework process, the rework method is incorrect, or the micro-etching time during the rework process is improperly controlled, etc., etc., or other reasons will cause the board surface to blist; If rework is found to be poor in copper deposits on the line, you can directly remove the oil from the line after washing with water and then directly rework without corrosion. Pay attention to the time control of the corrosion bath. You can first use one or two plates to roughly calculate the deplating time to ensure the deplating effect; after the deplating is completed, apply a set of soft brushes and lightly brush the plate and then follow the normal production process. Copper, but the etch and micro-etch time should be halved or adjusted if necessary;

Insufficient washing after development during the graphics transfer process, too long storage time after development or too much dust in the workshop, etc., will cause poor cleanliness of the board surface, and slightly poor fiber treatment effect, which may cause potential quality problems;

Before copper plating, the pickling tank should be replaced in time. Too much pollution in the bath or too high copper content will not only cause problems with the cleanliness of the board surface, but also cause defects such as rough board surface;

Organic pollution in the electroplating tank, especially oil pollution, is more likely to occur for automatic lines;

In addition, when the bath liquid is not heated in some factories in winter, it is necessary to pay special attention to the electrification of the plate during the production process, especially the plating tank with air agitation, such as copper and nickel; for nickel tanks, it is best to plate in winter. Add a heated washing tank before nickel (water temperature is about 30-40 degrees) to ensure that the initial deposition of the nickel layer is dense and good; ipcb is a high-precision and high-quality PCB manufacturer, such as: isola 370hr PCB, high-frequency PCB, High-speed PCB, ic substrate, ic test board, impedance PCB, HDI PCB, Rigid-Flex PCB, buried blind hole PCB, advanced PCB, microwave PCB, telfon PCB and other ipcb are good at PCB manufacturing.