PCB Tech - Analysis of the reason why there is no copper in the PCB hole sinking copper

Analysis of the reason why there is no copper in the copper sinking of the PCB board. The use of different resin systems and substrates with different resin systems will result in obvious differences in the activation effect of the copper sinking and the copper sinking.

In particular, some CEM composite substrates and high-frequency boards are specific to silver substrates. When electroless copper is processed, some special methods need to be taken. If normal electroless copper is used, it is sometimes difficult to achieve good results. Substrate pre-processing problems. Some substrates may absorb moisture and part of the resin itself is poorly cured when they are pressed into the substrate. This may result in poor drilling quality due to insufficient resin strength when drilling, excessive drilling dirt or tearing of the resin on the hole wall The digging is serious, so it must be baked when cutting the material. In addition, after some multi-layer boards are laminated, poor curing of branches in the base material area of the pp prepreg may also occur, which will directly affect drilling and slag removal and activation of copper sinks.

Poor drilling conditions, mainly manifested as: a lot of resin dust in the hole, rough hole walls, serious burrs in the holes, burrs in the holes, nail heads of the inner copper foil, uneven length of the torn section of the glass fiber area, etc., will cause chemical copper Certain quality hazards. In addition to mechanically removing the substrate surface contamination and removing the burrs/fronts of the pores, the brushing board performs surface cleaning.

In many cases, it also cleans and removes the dust in the pores. In particular, it is more important to treat more double-sided panels without the slag removal process.

There is another point to explain. Don’t think that you can get slag and dust out of the hole with the slag removal process. In fact, in many cases, the slag removal process has extremely limited dust treatment effects, because the dust in the tank liquid will form small glue. It is difficult to deal with the bath liquid. The micelle adsorbs on the hole wall and may form a plating tumor in the hole. It may also fall off from the hole wall during the subsequent processing. This may also cause no copper in the hole. In terms of layer and double-sided boards, the necessary mechanical brushing and high-pressure cleaning are also necessary, especially in the face of industry development trends, where small orifice boards and high aspect ratio boards are becoming more and more common. Even sometimes ultrasonic cleaning to remove dust in the hole has become a trend. Reasonable and appropriate de-smear process can greatly increase the hole ratio bonding force and the reliability of the inner layer connection, but the poor coordination of the de-glue process and related bath liquids will also bring some accidental problems. Insufficient slag removal will cause micro-holes in the hole wall, poor inner layer bonding, detachment of the hole wall, blow holes, etc.; excessive removal of glue may also cause the glass fiber in the hole to protrude, the hole is rough, the glass fiber is cut off, and the copper is infiltrated, The inner layer wedge-shaped hole breaks the separation between the inner layer of blackened copper, causing the hole copper to be broken or discontinuous, or the plating layer wrinkles and the plating layer stress increases.

In addition, the problem of coordinated control between several tanks for removing glue is also a very important reason. Insufficient bulking/swelling may result in insufficient slag removal; bulking/swelling transitions and it is more able to remove the already fluffy resin, then it will be activated when the copper is deposited, and the deposited copper will not be activated, even if the copper is deposited. Defects such as resin sinking and hole wall detachment may occur in the subsequent process; for the glue removal tank, the new tank and higher processing activity may also cause excessive removal of some monofunctional resins, bifunctional resins and some trifunctional resins. The glue phenomenon causes the glass fiber in the hole wall to protrude. The glass fiber is more difficult to activate and has a worse bonding force with the chemical copper than with the resin. After the copper is deposited, the chemical copper stress will be doubled and serious due to the deposition of the coating on the extremely uneven substrate. It can be clearly seen that the chemical copper on the hole wall after the copper sinking falls off from the hole wall, resulting in no copper in the subsequent hole. Holes without copper open circuit is no stranger to PCB industry people, but how to control it? Many colleagues have asked many times. I have done a lot of slicing, but the problem still cannot be completely improved. I always repeat it again and again. Today is caused by this process, and tomorrow is caused by that process. In fact, it is not difficult to control, but some people can't insist on supervision and prevention. The following is my personal opinion and control method of the hole without copper open circuit.

The reason for the hole-free copper is nothing more than:

1. Drilling dust plug holes or thick holes.

2. There are bubbles in the potion when the copper is sinking, and the copper is not sinking in the hole.

3. There is circuit ink in the hole, the protective layer is not electrically connected, and the hole is free of copper after etching.

4. The acid-base solution in the hole is not cleaned after the copper is deposited or after the board is powered on, and the parking time is too long, resulting in slow biting corrosion.

5. Improper operation, too long in the process of micro-etching.

6. The pressure of the punching plate is too high, (the design punching hole is too close to the conductive hole) and the middle is neatly disconnected.

7. Poor penetration of electroplating chemicals (tin, nickel).

Make improvements to these 7 reasons for the hole-free copper problem:

1. Add high-pressure water washing and de-smearing processes to holes that are prone to dust (such as 0.3mm or less aperture containing 0.3mm).

2. Improve potion activity and shock effect.

3. Change the printing screen and counterpoint film.

4. Extend the washing time and specify how many hours to complete the graphics transfer.

5. Set the timer.

6. Increase explosion-proof holes. Reduce the force on the circuit board.

7. Do penetration testing regularly.