Cause analysis of copper free in PCB hole copper deposition using different resin system and material base plate, different resin system will lead to significant difference in activation effect and copper deposition.
Especially for the specificity of some CEM composite plates and high frequency plates silver substrate, some special methods should be taken to deal with the chemical copper deposition. If the normal chemical copper deposition is used, it is sometimes difficult to achieve good results Pretreatment of baseplate some baseplates may absorb moisture and some resins will not cure well when they are pressed into the baseplate. In this way, the drilling quality may be poor due to the insufficient strength of the resin itself during drilling, and there may be too much drilling dirt or serious tearing of resin on the hole wall. Therefore, baking is necessary during cutting. In addition, some multilayer laminates may also have poor tree solidification in the substrate area of PP semi-cured sheet, which will also directly affect drilling and degumming slag activation copper deposition.
The drilling condition is too poor, mainly manifested as: there are many resin dust in the hole, rough hole wall, serious burr in the hole, burr in the hole, nail head of inner copper foil, uneven length of torn section in glass fiber area, etc., which will cause certain quality hazards to chemical copper In addition to mechanical treatment of substrate surface pollution and removal of orifice burr / plume, brush plate can clean the surface. In many cases, it can also clean and remove the dust in the hole. In particular, it is more important to treat the double-sided board without degumming slag.
It should also be noted that we should not think that the rubber residue and dust in the hole can be removed with the rubber residue. In fact, in many cases, the effect of the rubber residue removal process on dust treatment is extremely limited, because the dust in the tank liquid will form a small micelle, which makes the tank liquid difficult to deal with. The micelle may form a plating tumor in the hole wall when it is adsorbed on the hole wall, or it may fall off from the hole wall in the subsequent processing process In this way, there may be no copper in the hole. Therefore, it is also necessary for multi-layer and double-sided boards to have mechanical brush and high-pressure cleaning, especially facing the development trend of the industry. Small hole boards and high aspect ratio boards are becoming more and more common. Even sometimes ultrasonic cleaning to remove the dust in the hole has become a trend Reasonable and appropriate degumming slag technology can greatly increase the hole specific binding force and inner layer connection reliability, but the poor coordination between degumming technology and related tank fluid will also bring some accidental problems. The lack of degumming slag will cause micropores in the hole wall, poor inner layer bonding, hole wall separation, blowhole and other quality hazards; excessive degumming may also cause the glass fiber in the hole to protrude, the hole is rough, the glass fiber cut-off point, copper penetration, the inner wedge-shaped hole to break the inner layer of blackened copper to form the hole copper fracture or discontinuity, or the stress of the coating wrinkle increases.
In addition, the coordination and control between several tank fluids is also a very important reason Insufficient expansion / swelling may result in insufficient degumming residue; if the resin can be removed completely due to the transition of expansion / swelling, it will also activate the poor copper deposition during copper deposition. Even if copper deposition is carried out, the resin may sink in the subsequent process, and the hole wall may be detached; for the degumming tank, the new tank and the higher treatment activity may also result in some low connection degree of single functional resin Excessive degumming of dual-function resin and part of three-function resin results in protruding glass fiber on the hole wall, which is difficult to activate and has worse bonding force with chemical copper than with resin. After copper deposition, due to the deposition of coating on extremely uneven substrate, the stress of chemical copper will increase exponentially, and it can be seen that one piece of chemical copper on the hole wall will fall off from the hole wall after copper deposition, resulting in subsequent There is no copper in the hole No copper holes open circuit, PCB industry is not unfamiliar, but how to control? Many colleagues have asked many times. A lot of slicing has been done, but the problems still can't be completely improved. They always come back again and again. Today is the process, and tomorrow is the process. In fact, it is not difficult to control, but some people can not insist on supervision and prevention. They always have headache and foot pain The following is my personal opinion and control method of copper free open circuit.
The reasons for copper free holes are as follows:
1. The dust plug hole or hole diameter shall be drilled.
2. There are bubbles in the solution during copper deposition, and copper is not deposited in the hole.
3. There is line ink in the hole, no protective layer is applied, and there is no copper in the hole after etching.
4. After copper deposition or plate electricity, the acid and alkali solution in the hole is not cleaned, and the storage time is too long, resulting in slow corrosion.
5. Improper operation, too long stay time in micro etching process.
6. The punching plate pressure is too large (the designed punching hole is too close to the conductive hole) and the middle part is orderly disconnected.
7. Poor penetration of electroplating solution (tin, nickel).
To solve the problem of copper free in these 7 holes, the following measures were taken:
1. Add high-pressure water washing and degumming process to holes prone to dust (for example, the hole diameter below 0.3mm contains 0.3mm).
2. Improve the activity and concussion effect of the liquid medicine.
3. Change printing screen and alignment film
4. Extend washing time and specify how many hours to complete graphic transfer
5. Set the timer.
6. Add explosion-proof holes. Reduce the force on the board.
7. Conduct permeability test regularly.
Sep 12, 2019
