Analysis on Copper Fall off from Flex PCB

Different reasons will cause copper come off from flexible PCB, here we analyze this phenomenon from manifacturing process and raw material aspect:

Manufacturing  Process:

Under normal circumstances, the copper foil and the prepreg will be basically completely bonded as long as the high temperature section of the laminate is hot pressed for more than 30 minutes, so the pressing will generally not affect the bonding force of the copper foil and the substrate in the laminate. However, in the process of stacking and stacking laminates, if the PP is contaminated or the matte surface of the copper foil is damaged, it will also cause insufficient bonding between the copper foil and the substrate after lamination, resulting in positioning (only for large plates) Words) or sporadic copper wires fall off, but the peeling strength of the copper foil near the off wires will not be abnormal.

Raw Materials:

1. As mentioned above, ordinary electrolytic copper foils are all products that have been galvanized or copper-plated. If the peak value of the wool foil is abnormal during production, or when galvanized/copper-plated, the plating crystal branches are bad, causing the copper foil itself The peeling strength is not enough. When the bad foil pressed sheet material is made into PCB and plug-in in the electronics factory, the copper wire will fall off due to the impact of external force. This kind of poor copper rejection will not cause obvious side corrosion after peeling the copper wire to see the rough surface of the copper foil (that is, the contact surface with the substrate), but the peeling strength of the entire copper foil will be very poor.

2.Poor adaptability of copper foil and resin: Some laminates with special properties, such as HTg sheets, are used now. Because of different resin systems, the curing agent used is generally PN resin, and the resin molecular chain structure is simple. The degree of cross-linking is low, and it is necessary to use a copper foil with a special peak to match it. When producing laminates, the use of copper foil does not match the resin system, resulting in insufficient peeling strength of the sheet metal-clad metal foil, and poor copper wire shedding when inserting.