The drilling condition of printed circuit boards for communication is too bad. The main performances are: more resin dust in the hole, rough hole wall, serious hole burr, hole burr, inner copper foil nail head, uneven length of tear section in glass fiber area, which will cause certain quality hidden danger to chemical copper. Brush board uses mechanical method to deal with the surface contamination of the substrate, remove burrs and pipes at the orifice, and clean the surface. In many cases, it also plays the role of cleaning and removing dust in the hole. Especially, it is more important for the double panels which are not treated by the degumming slag process.
It should also be pointed out that people should not think that the rubber residue and dust can be removed from the hole with the rubber residue removed. In fact, in many cases, the dust removal process has very limited effect on the dust treatment, because the dust in the tank solution will form small micelles, which make the tank solution difficult to handle. The micelle adsorbed on the hole wall may form a hole plating tumour. It is also possible to peel off the hole wall in the subsequent processing, which may also result in copper-free dots in the hole. Therefore, for multi-layer and double panels, it is necessary to brush the machine and clean them under high pressure. Especially, it is facing the development trend of the industry. Small hole panels and high aspect ratio panels are becoming more and more common. Sometimes even the removal of dust in holes by ultrasonic cleaning has become a trend. Reasonable and appropriate degumming slag process can greatly increase the hole ratio binding force and the reliability of inner connection, but the poor coordination between degumming process and related tank liquids will also bring some accidental problems. Insufficient degumming slag will cause potential quality hazards such as hole wall microvoids, poor internal bonding, hole wall detachment, blow holes and so on. Excessive de-gluing may also result in protrusion of glass fibers in holes, roughness in holes, cut-off points of glass fibers, copper infiltration, separation of inner wedge-shaped holes and inner blackened copper, result in fracture or discontinuity of porous copper, or increase stress of plating folds and coatings.
In addition, the problem of coordinated control among several tank fluids is also a very important reason. The expansion or insufficient swelling of communication PCB board may result in insufficient degumming slag; the transition between bulking and swelling can remove all the fluffy resin, and then the inactive precipitation of copper will not be activated when copper is deposited, even if copper is deposited, resin subsidence and hole wall detachment may occur in the later process; for the degumming tank, the new tank and the comparison are made. High treatment activity may also result in excessive de-gluing of some unifunctional resin bifunctional resins and some trifunctional resins with lower bonding degree, which leads to the prominence of pore wall glass fibers, the difficulty of activation of glass fibers and the worse bonding force with chemical copper than with resins. Copper stress will be doubled. It is obvious that chemical copper sheets fall off from the hole wall after copper sinking, resulting in no copper in the subsequent hole. Here are some simple summaries:
The main reasons for copper-free perforation of printed circuit boards for communication are as follows:
1. Drilling dust plug hole or hole diameter.
2. When copper is deposited, there are bubbles in the liquid medicine, and copper is not deposited in the hole.
3. There is line ink in the hole, no electric protective layer and no copper in the etched hole.
4. After copper precipitation or plate electrolysis, the acid-base potion in the hole is not cleaned, and the stopping time is too long, resulting in slow biting.
5. improper operation and too long residence time in Micro-etching process.
6. The pressure of punching plate is too high (the design punch is too close to the conductive hole) and the middle of the punch is neatly disconnected.
7. The penetration ability of electroplating solution (tin and nickel) is poor.
In view of the causes of the seven problems of copper-free pore formation, some improvements are made.
1. Adding high-pressure washing and deburring processes to dust-prone holes (e.g. holes less than 0.3mm with a diameter of 0.3mm).
2. Enhance the activity and shock effect of the liquid medicine.
3. Printing screen and counterpart film.
4. Extend the washing time and specify how many hours to complete the graphic transfer.
5. Set a timer.
6. Increase explosion-proof holes and reduce the force on the plate.
7. Perform permeability tests regularly.