PCB News - PCB, flexible and hard board hole wall plating cavity

Causes and Countermeasures of Hole Wall Plating Holes in PCB and Rigid-Flex Board
Electroless copper is a very important step in the metallization process of PCB and soft and hard bonding board holes. The goal is to form a very thin conductive copper layer on the hole wall and copper surface to prepare for the subsequent electroplating.

The vacancy of the hole wall plating is one of the common deficiencies in the metallization of PCB board and soft and hard joint board holes, and it is also one of the items that easily induces the mass scrapping of printed circuit boards, because this solves the problem of printed circuit board plating vacancies in the printed circuit board. The manufacturer focuses on an internal substantive meaning, but because there are many reasons for its deficiency, only the correct judgment of its lack of characteristics indicates that the ability to find a solution is effective.

1. Hole wall coating voids caused by PTH PTH-induced void wall coatings are mainly dotted or ring-shaped voids. The specific causes of initiation are as follows:

(1) The temperature of the bath The temperature of the bath also has an important influence on the activity of the solution. There are generally temperature requirements in each solution, and there is something to be strictly controlled. Therefore, the temperature of the bath liquid should also be watched at any time.

(2) Restriction of the activation solution The low divalent tin ions will cause the decomposition of colloidal palladium and affect the adsorption of palladium, but as long as the activation solution is regularly supplemented, it will not cause major problems. The key point of activating liquid control is that it cannot be mixed with air. The oxygen in the air will oxidize the divalent tin ions, and at the same time, no water can enter, which will cause the water decomposition of SnCl2.

(3) Cleaning temperature The cleaning temperature is often overlooked. The best cleaning temperature is above 20°C. If it is lower than 15°C, the cleaning effect will be affected. In the cold winter, the water temperature will become very low, especially in the north. Because the temperature of water washing is low, the temperature of the wrench after cleaning will also become very low. After entering the copper cylinder, the temperature of the wrench cannot rise up, as it will lose the gold time of the copper siltation and affect the effect of the siltation. Therefore, in places where the background temperature is low, pay attention to the temperature of the cleaning water.

(4) The application temperature, liquid concentration and time of the pore modifier have strict requirements on the temperature of the liquid medicine. Excessive temperature will cause the pore modifier to decompose, and the liquid concentration of the pore modifier will become lower, which will affect the integrity of the pore. The effect, the characteristic mark of its surfaceization is that dotted voids appear at the glass fiber cloth in the hole. Only if the temperature, liquid concentration and time of the liquid medicine are properly appropriate, the ability to obtain a satisfactory pore size effect can also save costs. The concentration of copper ionic liquid that continues to accumulate in the chemical solution must also be strictly controlled.

(5) Application temperature, liquid concentration and time of the recovery agent. The effect of recovery is to remove the potassium manganate and potassium permanganate left after the drilling dirt is removed. The out-of-control of the relevant parameters of the liquid medicine will affect its effectiveness. The characteristic mark is that dots are exposed at the natural resin in the hole.

(6) Vibrator and shaking The loss of control of the vibrator and shaking will lead to ring-shaped voids. This is mainly because the bubbles in the holes cannot be eliminated. The perforated plates with high thickness to diameter ratio are the most superficial. The characteristic sign of its surfaceization is the sparseness and symmetry in the hole, and the copper thickness of the part with copper in the hole is normal, and the pattern plating layer (secondary copper) wraps the entire board plating layer (primary copper).

2. Hole wall plating caused by pattern transfer is sparse

The voids in the hole wall plating caused by pattern transfer are mainly the ring-shaped orifice and the ring-shaped void in the hole. The specific causes of initiation are as follows:

(1) Pre-treatment of the brush plate. The pressure of the brush plate is too high, and the copper layer at the copper and PTH holes of the whole plate is rubbed off by the brush, so that the subsequent pattern plating cannot be plated with copper, so a ring-shaped hole is formed. The characteristic sign of its surfaceization is that the copper layer of the orifice gradually changes and becomes thinner, and the pattern plating layer wraps the entire plate plating layer. Therefore, it must undergo a wear scar test to control the pressure of the brush plate.

(2) The residual glue at the orifice is very close to the control of the process parameters in the pattern transfer process. Due to poor pre-treatment baking, improper temperature and pressure of the film, the edge of the orifice will be exposed to residual glue and cause the orifice. The annular space is sparse. The characteristic sign of its surfaceization is that the thickness of the copper layer in the hole is normal, a ring-shaped void flashes at the mouth of one or two faces, extending to the pad, and there are surfaced and etched residues on the edge of the fault, and the pattern plating layer does not cover the entire board.

(3) Pre-treatment micro-etching The amount of pre-treatment micro-etching should be strictly controlled, especially the number of reworking cycles of dry film panels. The main reason is that the thickness of the plating layer in the middle of the hole is too thin due to the problem of plating uniformity. Too much reworking will result in the thinning of the copper layer in the whole board hole, and finally the ring-shaped copper-free head in the hole will be formed. The characteristic sign of its surfaceization is that the plating layer of the whole plate in the hole gradually changes and becomes thinner, and the pattern plating layer wraps the whole plate plating layer.

3. Hole wall plating caused by pattern plating is sparse

(1) Pattern electroplating micro-etching The amount of pattern plating micro-etching should also be strictly controlled, and the initiation of defects is basically the same as the micro-etching before dry film treatment. In severe cases, the hole wall will be large or the size of the surface of the object will be copper-free, and the thickness of the entire board on the board will be thinner. Therefore, to regularly measure the micro-etching efficiency, it is best to optimize the process parameters through the implementation of the DOE experiment.

(2) Poor dispersibility of tin plating (lead-tin) due to poor solution performance or insufficient shaking, etc., the thickness of the tin plating layer is insufficient, and the tin layer and copper layer in the middle of the hole are removed during the subsequent film removal and alkaline etching. Eroded, an annular space sparsely sprouted. The characteristic sign of surfaceization is that the thickness of the copper layer in the hole is normal, there are traces of surfaceization and corrosion on the edge of the fault, and the pattern plating layer does not cover the entire board. In view of this situation, a little tinning brightener can be added to the pickling before tinning, which can increase the wettability of the wrench and at the same time increase the amplitude of shaking.

4. Judgment There are many factors that lead to the vacancy of the coating, the most common one is the vacancy of the PTH coating. The relevant process parameters of the pharmaceutical industry can effectively reduce the initiation of the vacancy of the PTH coating. However, other factors should not be ignored. Only after careful and careful inspection, we understand the reasons for the sparse coating and the unique places that are lacking, and the ability to solve the problem as early as possible and protect the quality of the product.

The above is an introduction to the causes and countermeasures of the holes in PCB and rigid-flex board hole wall coatings and countermeasures. Ipcb also provides PCB manufacturers and PCB manufacturing technology.