Cause Analysis of No Copper in Holes of PCB Board Immerse Copper
The use of different resin systems and material substrates, different resin systems, will cause significant differences in the activation effect of Immerse Copper treatment and Immerse Copper. In particular, some CEM composite substrates and high-frequency silver substrates are specific. When chemical Immerse Copper is treated, some special methods need to be taken. If normal chemical Immerse Copper is sometimes difficult to achieve good results.
Pre-treatment of substrates
Some substrates may absorb moisture and poorly solidify some resins when pressed into a synthetic substrate. In this case, the drilling quality may be poor due to the insufficient strength of the resin itself, and there may be excessive drilling stains or severe resin tearing on the hole wall. Therefore, the necessary baking should be performed when opening. In addition, some multilayer boards may also suffer from poor curing of the branches in the pp prepreg base material area after lamination, which will directly affect the drilling and activation of Immerse Copper.
Poor drilling conditions are mainly manifested as: excessive resin dust in the hole, rough hole wall, severe burr in the hole, burr in the hole, inner copper foil nail head, uneven length of the tear section in the glass fiber area, etc., which will cause chemical copper. Certain quality risks.
In addition to mechanically treating the substrate surface to remove contamination on the substrate and removing burrs / clutters on the orifice, the brush plate cleans the surface. In many cases, it also plays a role in cleaning and removing dust in the hole. In particular, it is more important to deal with double-sided panels without the slag removal process.
It is also important to point out that you should not think that you can get out of the slag and dust in the hole with the slag removal. In fact, in many cases, the slag removal process has a very limited effect on dust treatment, because the dust in the bath will form small glue. This makes the bath difficult to handle. This gel may form a nodule in the hole when it is adsorbed on the hole wall, or it may fall off from the hole wall during subsequent processing. This may also cause the point-like copper-free inside the hole. In terms of layers and double-sided boards, the necessary mechanical brushing and high-pressure cleaning are also required, especially in the face of industry development trends. Small-hole plates and high aspect ratio boards are becoming more and more common. In some cases, it is also a trend to remove dust in the holes by ultrasonic cleaning.
Reasonable and appropriate de-slagging process can greatly increase the hole-to-specific ratio binding force and the reliability of the inner layer connection, but the problem of poor coordination between the de-sizing process and related tank fluids will also bring some occasional problems. Insufficient glue removal will cause micro-holes in the hole wall, poor inner layer bonding, detachment of the hole wall, blow holes, and other quality hazards. Excessive glue removal may also cause the glass fibers in the holes to protrude, the holes to be rough, glass fiber intercept points, and copper infiltration , The inner layer of the wedge-shaped hole breaks the inner layer of blackened copper, causing the hole copper to break or discontinue, or the plating wrinkle to increase the stress of the coating. In addition, the problem of coordinated control between several degumming baths is also very important.
Insufficient bulking / swelling may result in insufficient removal of rubber residue. The bulky / swelling transition can be used to remove the fluffy resin, so it will be activated badly when Immerse Copper is changed. Defects such as resin sags and detachment of pore walls in the later steps; for the glue removal tank, the new groove and higher processing activity may also cause some of the lower degree of single-functional resin, dual-functional resin, and some three-functional resins to be excessively removed This phenomenon causes the glass fiber on the hole wall to protrude. The glass fiber is harder to activate and has a worse binding force with the chemical copper than the resin. After the copper is deposited, the chemical copper stress will be doubled due to the deposition of the coating on the extremely uneven substrate. Obviously, after the Immerse Copper, the chemical copper on the hole wall was peeled off from the hole wall, causing no copper in the subsequent holes.
Holes without copper are no strangers to the PCB industry, but how to control them? Many colleagues have asked many times. A lot of slicing has been done, and the problem still cannot be completely improved. It always repeats itself. Today is caused by this process, and tomorrow it is caused by that process. In fact, control is not difficult, it is just that some people cannot insist on supervision and prevention.
The following are my personal opinions and control methods for copper-free open circuit. The reason for producing copper without holes is nothing more than:
1. Drilling dust plug holes or thick holes.
2. There are bubbles in the potion of Immerse Copper, and there is no Immerse Copper in the hole.
3. There is circuit ink in the hole, no protective layer is applied, and there is no copper in the hole after etching.
4. After the Immerse Copper or the board is charged, the acid and alkali solution in the hole is not cleaned, and the parking time is too long, resulting in slow bite.
5. Improper operation, too long residence time during micro-etching.
6. The punching plate pressure is too high, and the design punching hole is too close to the conductive hole.
7. The plating solution (tin, nickel) has poor permeability.
To improve the causes of copper-free holes in these 7 major problems:
1. Increase the high-pressure water washing and slag removal processes for holes that are prone to dust (such as 0.3mm below 0.3mm).
2. Improve potion activity and shock effect.
3.Change printing screen and counter film.
4.Extend the washing time and specify the number of hours to complete the graphics transfer.
5. Set the timer.
6. Add explosion-proof holes. Reduce the force on the board.
7. Do penetration tests regularly.