Analysis of three reasons for PCB copper rejection
In terms of PCB copper loss (also often said that the rejection of copper) defect, PCB plant says that this is caused by bear and asks for compensation. According to years experience in dealing with customer complaints, common reasons of PCB copper rejection are the following:
1. PCB factory process factors:
(a)copper etched over, electrolytic copper foil used on the market generally sided galvanized steel (commonly known as ash foil) and single-sided copper (commonly known as the red of the foil), a common rejection of copper is generally above 70um copper galvanized foil, foil and 18um reddening following ashing foil basic none appeared bulk of the rejection of copper. Customer circuit design is better than etching line, if the copper foil after the specification change and etch parameters unchanged, resulting in a copper foil in the etching solution too long the residence time. Zinc was originally due to active metal, copper on the PCB when a long soak in the etching solution, will lead the line side excessive erosion, causing some of the fine line backing zinc layer is completely reacted with the substrate detachment, namely copper off. Another case is PCB etching parameters is no problem, but after etching poor washing and drying, resulting in a copper etching solution also will face surrounded PCB residues in untreated for a long time, will produce excessive side etching copper rejection of copper. This is usually expressed as concentrated in a thin line on the road, or a period of wet weather, the entire PCB will appear similar to the bad, look at it with the grass roots ripping copper contact surface (the so-called rough surface) color has changed, normal copper color is not the same, see the bottom of the original copper color, thick line at the copper peel strength is also normal.
(b)collision occurs locally PCB process, copper wire by external mechanical forces from the substrate. This poor performance is poor positioning or fixed directional, there will be significant copper twisted off, or the same direction to scratch / impact marks. Look at the copper foil peel bad hair surface, you can see the color of copper matte is normal, there will be no adverse side etching, copper peel strength is normal.
(c)PCB circuit design is unreasonable, meticulous design with thick copper lines, can also cause excessive rejection lines etched copper.
2. the laminate manufacturing process reasons:
Under normal circumstances, as long as the laminate after hot pressing high temperature section over 30min, copper foil and the prepreg is substantially completely the binding, so nip generally will not affect the binding force of the copper foil laminate and the substrate. However, with the laminate stack, the stacking process, if PP contamination, or damage to the matte side of the copper foil will lead to insufficient adhesion after lamination of the copper foil and the substrate, resulting in the positioning (only for large plate words) or sporadic copper off, but near the copper peel strength measured off-line will not be an exception.
3. the laminate material reasons:
(a) the above mentioned are ordinary electrolytic copper foil hair galvanized or copper-treated products, if the hair foil production peak is abnormal, or zinc / copper, the coating dendrites bad, causing copper itself peel strength is not enough, the poor material made of pressed board after the foil off PCB will take place at the electronics factory plug-in, copper by external shocks. Such rejection of copper foil hair look bad ripping copper surface (ie, contact with the substrate surface) is not obvious side after pitting, but the entire surface of the copper foil peel strength will be poor.
(b) the copper foil and resin poor adaptability: some special properties of the laminate are now used, such as HTg sheet, because the resin system is not the same, the curing agent is generally used PN resin, a simple resin molecular chain structure, upon curing a low degree of crosslinking, is bound to use a special foil peak match. When the production of laminates using the copper foil and the resin system does not match, causing the sheet metal-clad peel strength is not enough, there will be bad when copper plug off.