In the production process of PCB circuit boards, some process defects are often encountered, such as poor copper wire fall off of PCB circuit boards (also known as copper rejection), which affects product quality. The common reasons for copper rejection of PCB circuit boards are as follows:
PCB Circuit Board Process Factors:
1. The copper foil is over-etched. The electrolytic copper foil used in the market is generally single-sided galvanized (commonly known as ashing foil) and single-sided copper-plated (commonly known as reddish foil). The common copper rejection is generally galvanized copper above 70um Foils, red foils and ashing foils below 18um have basically not experienced batch copper rejection.
2. A local collision occurs in the PCB process, and the copper wire is separated from the substrate by external mechanical force. This defect is manifested as poor positioning or orientation, and there will be obvious twists in the dropped copper wire, or scratches/impact marks in the same direction. Peel off the bad copper wire and look at the rough surface of the copper foil. It can be seen that the color of the rough surface of the copper foil is normal, there will be no bad side corrosion, and the peeling strength of the copper foil is normal.
3. The PCB circuit design is unreasonable. Designing too thin circuits with thick copper foil will also cause excessive circuit etching and copper rejection.
Laminate Process Reasons:
Under normal circumstances, as long as the laminate is hot-pressed for more than 30 minutes in the high temperature section, the copper foil and the prepreg are basically completely combined, so the pressing generally does not affect the bonding force between the copper foil and the substrate in the laminate. However, in the process of stacking and stacking laminates, if PP is polluted, or the rough surface of copper foil is damaged, it will also lead to insufficient bonding force between copper foil and substrate after lamination, resulting in positioning (only for large boards and language) or sporadic copper wires fall off, but there is no abnormality in the peeling strength of copper foil near the disconnected wires.
Laminate Raw Material Reasons:
1. Ordinary electrolytic copper foils are galvanized or copper-plated wool foil products. If the wool foil is produced with an abnormal peak value, or when galvanized/copper-plated, the coating dendrites are not good, resulting in insufficient peel strength of the copper foil itself. , When the bad foil pressed sheet is made into circuit board and inserted in the electronics factory, the copper wire will fall off under the impact of external force. This kind of poor copper rejection will not cause obvious side etching after peeling the copper wire to see the rough surface of the copper foil (that is, the surface in contact with the substrate), but the peeling strength of the copper foil on the whole surface will be very poor.
2. Poor adaptability between copper foil and resin: Some laminates with special properties currently used, such as HTg sheets, are generally PN resins as curing agents due to different resin systems. The resin molecular chain structure is simple, and when curing The degree of crosslinking is low, and it is necessary to use copper foil with special peaks to match it. When producing laminates, the use of copper foil does not match the resin system, resulting in insufficient peel strength of the metal-clad sheet metal foil, and poor copper wire falling off when inserting.