The copper wire of the PCB falls off (that is, the copper is often said to be thrown away), and each PCB brand will infer that it is the problem of the laminate, requiring its production factory to bear the bad losses. According to years of experience in handling customer complaints, the common reasons for PCB copper rejection are as follows:
1. PCB factory process factors:
a. The copper foil is over-etched.
The electrolytic copper foils used in the market are generally single-sided galvanized (commonly known as ashing foil) and single-sided copper-plated (commonly known as reddish foil). The following ashing foils basically did not experience batch copper rejection. When the circuit is designed to pass the etching line, if the copper foil specification is changed but the etching parameters are not changed, the copper foil will stay in the etching solution for a long time.
Because zinc is an active metal, when the copper wire on the PCB is immersed in the etching solution for a long time, it will cause excessive side etching of the circuit, causing the backing zinc layer of some thin circuits to be completely reacted and separated from the substrate, that is, The copper wire fell off.
Another situation is that there is no problem with the PCB etching parameters, but the washing and drying after etching are not good, causing the copper wire to be surrounded by the etching solution left on the PCB surface. copper.
This situation is generally concentrated on thin lines, or when the weather is wet, similar defects will appear on the entire PCB. Strip the copper wire to see that the color of the contact surface with the base layer (the so-called roughened surface) has changed, which is different from the normal copper wire. The color of the foil is different, the original copper color of the bottom layer is seen, and the peeling strength of the copper foil at the thick circuit is also normal.
b. A local collision occurs in the PCB production process, and the copper wire is separated from the base material by mechanical external force.
There is a problem with the positioning of this poor performance, and the falling copper wire will have obvious distortion, or scratches or 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.
c. The PCB circuit design is unreasonable.
Designing too thin lines with thick copper foil will also cause the lines to be over-etched and copper to be thrown away.
2. Reasons for the laminate process:
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 lamination 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 the PP is contaminated or the rough surface of the copper foil is damaged, it will also lead to insufficient bonding force between the copper foil and the substrate after lamination, resulting in positioning deviation (only for large boards). ) or sporadic copper wires fall off, but there is no abnormality in the peeling strength of copper foil near the disconnected wires.
3. Reasons for laminate raw materials:
a. As mentioned above, ordinary electrolytic copper foils are all galvanized or copper-plated wool foil products. If the wool foil is produced with abnormal peaks, or when galvanized/copper-plated, the coating dendrites are not good, causing the copper foil itself. The peel strength is not enough. When the defective foil pressed sheet is made into a PCB and inserted in an electronic factory, the copper wire will fall off under the impact of external force. This kind of poor copper throwing off the copper wire to see that the rough surface of the copper foil (that is, the contact surface with the substrate) will not have obvious side corrosion, but the peel strength of the copper foil on the entire surface will be very poor.
b. 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 degree of crosslinking is low, and it is necessary to use copper foil with special peaks to match it. When the copper foil used in the production of the laminate does not match the resin system, the peeling strength of the sheet metal-clad foil is not enough, and the copper wire will also fall off badly when inserting.
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