The production and response of the cavity of PCB hole wall

The chemical sink is a very important step in the process of PCB hole metallization. The purpose is to form a very thin conductive copper layer on the hole wall and copper surface to prepare for the later plating.And hole wall coating hole is one of the common defects of PCB hole metallization, easy cause batch printed circuit boards scrap is one of the project, therefore solve the problem of PCB plating cavity is one of the key control PCB manufacturer, but due to various causes of the defects, only accurately judge the defect characteristics can effectively find out the solutions.

1. The hole wall plating layer caused by PTH.

The hole wall coating hole caused by PTH is mainly a dot or ring hole, and the specific reasons are as follows:

(1) concentration of copper content, sodium hydroxide and formaldehyde in copper cylinder.

The solution concentration of the copper cylinder is the first consideration.Generally speaking, the copper content, sodium hydroxide and the concentration of formaldehyde is proportional to, when any one of them with the content of less than 10% of the standard numerical will destroy the balance of the chemical reaction, chemical copper deposit harmful, dot hole.Therefore, priority should be given to adjusting the parameters of the copper cylinder.

(2) the temperature of the tank solution.

The temperature of the bath has an important influence on the activity of the solution.There is usually a temperature requirement in each solution, some of which are strictly controlled.So you have to pay attention to the temperature of the tank.

(3) control of activated liquid.

The low divalent tin ion can cause the decomposition of palladium and affect the adsorption of palladium, but it will not cause big problems as long as it is added to the activated liquid regularly.The key point of the activation liquid control is that the air cannot be stirred by air, and the oxygen in the air can oxidize the divalent tin ion, but also cannot enter the water, resulting in the hydrolysis of SnCl2.

(4) temperature of cleaning.

Cleaning temperature often ignored, cleaning is the best temperature above 20 ℃, if below 15 ℃ can affect the effect of cleaning.In winter, the water temperature will be very low, especially in the north.Due to water temperature is low, the board after washing temperature will become very low, after entering the copper cylinder board temperature rises not immediately, because missed the gold copper deposition time and influence the effect of deposition.Therefore, in the lower environment temperature, also pay attention to the temperature of washing water.

(5) the use temperature, concentration and time of the rectifier.

The temperature of the liquid has a strict requirements, high temperature can cause the decomposition of the whole hole agent, make the concentration of the whole hole become low, influence the effect of the hole, its obvious feature is appeared at the hole of the glass fiber cloth dot is empty.Only when the temperature, concentration and time of the liquid are properly coordinated, can the whole hole effect be obtained, and the cost can be saved at the same time.The accumulated copper ion concentration in the solution must also be strictly controlled.

(6) the use temperature, concentration and time of reducing agent.

Reduction is used to remove residual potassium manganate and after drilling sewage of potassium permanganate, solution related parameters will influence the effect of out of control, its obvious feature is appeared in the hole of the resin cast hollow.

(7) oscillators and oscillations.

Oscillators and uncontrollable shaking can cause a ring hole, which is mainly due to the failure of the bubbles in the hole, which is most obvious in the hole with a high diameter ratio.The obvious feature is the hollow symmetry in the hole, while the copper in the hole is normal, and the electroplating layer (secondary copper) is coated with the whole plate (once copper).

2. Hole wall coating caused by graphic transfer.

The hole wall coating holes caused by the graphic transfer are mainly the holes in the ring and the ring in the hole, and the specific reasons are as follows:

(1) pretreatment brush plate.

The pressure of the brush plate is too high, and the copper layer on the copper and PTH orifice of the whole plate is brushed away, so that the latter can not be plated with copper, resulting in a ring hole in the orifice.The obvious characteristic is that the copper layer of the orifice is gradually thinning, and the electroplating layer is coated with the whole plate.Therefore, it is necessary to control the pressure of the brush plate through the grinding test.

(2) orifice residue.

In graphic transfer process control of the process parameters is very important, because treatment before drying, the temperature of the lamination, the wrong pressure leads to the edge of the orifice area in residue caused by orifice ring hollow.Its obvious characteristic is the thickness of copper in hole is normal, single or double orifice ring hollow, extends to the bonding pad, edge of fault have obviously been etched traces and graphic plating without full board package.

(3) pretreatment of microerosion.

The pretreatment of the microerosion should be strictly controlled, especially the rework of the dry film plate.It is mainly due to the thickness of the electroplating uniformity in the middle of the hole, the thickness of the plating layer is thin, and the overwork will cause the copper layer in the whole plate hole to be thinner, and in the end, there is no copper in the middle of the hole.The obvious feature is that the plating layer in the hole is gradually thinning, and the graphics electroplating layer is coated with the whole plate.

3. Hole wall plating caused by graphic electroplating.

(1) graphical electroplating microerosion.

The microcorrosion of graphic electroplating is also strictly controlled, and its defects are basically the same as that of pretreatment.When the wall is serious, there is no copper, and the thickness of the plate is obviously thin.Therefore, it is better to optimize the process parameters by conducting the DOE experiment.

(2) the dispersion of tin (lead tin) is poor.

Due to the poor performance of the solution or the lack of sway, the coating thickness of tin plating is insufficient, and the tin and copper layers in the middle of the hole are eroded away in the film and alkaline etching at the back, resulting in a ring cavity.The obvious feature is that the copper layer in the hole is of normal thickness, with obvious etching marks on the edge of the fault, and the graphics electroplating layer does not contain the whole plate (see figure 5).In this case, it is possible to add some tinning agent in the pre-tin dip acid, which can increase the wettability of the board and increase the amplitude of the swing.

4, the conclusion

There are many factors causing the hole in the coating, the most common is the PTH coating cavity, and the production of PTH coating cavity can be effectively reduced by controlling the related technological parameters of the potion.However, other factors can not be ignored. Only through careful observation and understanding of the causes and defects of the coating holes can we solve the problems and maintain the quality of the products in a timely and effective manner.