A. PCB factory process factors
1. Excessive etching of copper foil
The electrolytic copper foil used in the market is generally single-sided galvanized (commonly known as ashing foil) and single-sided copper plating (commonly known as red foil). The common copper foil is generally galvanized copper foil above 70um, red foil and 18um. The following ashing foil has basically no batch copper rejection. When the circuit design is better than the etching line, if the copper foil specification changes but the etching parameters do not change, this will make the copper foil stay in the etching solution too long.
Because zinc is originally an active metal, when the copper wire on the PCB is soaked in the etching solution for a long time, it will cause excessive side corrosion of the line, causing some thin line backing zinc layer to be completely reacted and separated from the substrate, that is, The copper wire falls off.
Another situation is that there is no problem with the PCB etching parameters, but the washing and drying are not good after etching, causing the copper wire to be surrounded by the remaining etching solution on the PCB surface. If it is not processed for a long time, it will also cause excessive copper wire side etching and rejection. copper.
This situation is generally concentrated on thin lines, or when the weather is humid, similar defects will appear on the entire PCB. Strip the copper wire to see that the color of its contact surface with the base layer (the so-called roughened surface) has changed, which is different from normal copper. The foil color is different. What you see is the original copper color of the bottom layer, and the peel strength of the copper foil at the thick line is also normal.
2. A local collision occurred in the PCB production process, and the copper wire was separated from the substrate by mechanical external force
This bad performance has a problem with positioning, and the copper wire will be obviously twisted, or scratches or impact marks in the same direction. Peel off the copper wire at the defective part and look at the rough surface of the copper foil, you can see 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. Unreasonable PCB circuit design
Designing thin circuits with thick copper foil will also cause excessive etching of the circuit and dump copper.
B.The reason for the laminate process
Under normal circumstances, the copper foil and the prepreg will be basically completely combined 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 PP contamination or copper foil rough surface damage, it will also lead to insufficient bonding force between copper foil and substrate after lamination, resulting in positioning deviation (only for large plates) ) Or sporadic copper wires fall off, but the peel strength of the copper foil near the off-line is not abnormal.
C. Reasons for laminate raw materials:
1. As mentioned above, ordinary electrolytic copper foils are all products that have been galvanized or copper-plated on the wool foil. If the peak value of the wool foil is abnormal during production, or when galvanizing/copper plating, the plating crystal branches are poor, causing the copper foil itself The peeling strength is not enough. After the bad foil pressed sheet material is made into PCB, the copper wire will fall off due to the impact of external force when it is plug-in in the electronics factory. This kind of poor copper rejection will not have obvious side corrosion when peeling the copper wire to see the rough surface of the copper foil (that is, the contact surface with the substrate), but the peel strength of the whole 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 the resin system is different, the curing agent used is generally PN resin, and the resin molecular chain structure is simple. The degree of crosslinking is low, and it is necessary to use copper foil with a special peak to match it. The copper foil used in the production of laminates does not match the resin system, resulting in insufficient peel strength of the sheet metal-clad metal foil, and poor copper wire shedding when inserting.