Electronic Design - PCB design and the reasons for the copper wire falling off

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2. Why does the copper wire of the impedance PCB circuit board fall off?

It is not good for the copper wire of the PCB circuit board to fall off (also known as copper throwing). It is said that the PCB factory is a laminate problem, and its production factory is required to bear bad losses.

Based on years of experience in handling customer complaints, common reasons for copper ingots in PCB factories are as follows:

Reasons for the copper wire of the impedance PCB circuit board to fall off

One, PCB circuit board factory process factors:

1. The copper foil is too etched. The electrolytic copper foil used in the market is generally single-sided galvanized (commonly known as gray foil) and single-sided copper (commonly known as red foil). Common copper dumps are generally more than 70um galvanized copper foil, The red foil and the gray foil below 18um basically did not appear in the copper batch. When the customer line design is better than the etching line, if the copper foil specification changes and the etching parameters remain unchanged, the residence time of the copper foil in the etching solution will be too long.

Because zinc is originally a kind of active metal, when the copper wire on the copper wire is in the etching solution for a long time, it will cause excessive lateral corrosion of the circuit, and cause some thin wire backing zinc layer to be fully reflected and separated from the substrate, that is, copper The thread falls off. There is another case that the etching parameters of the PCB circuit board are okay, but after etching, the washing and drying are not good, causing the copper wire to be surrounded by the etching solution on the surface of the PCB circuit board. If it has not been treated for a long time, it will also cause excessive corrosion of the copper edge. Throw copper. This situation is generally manifested in the concentration of thin lines on the road, or during wet weather, the entire PCB circuit board will have similar defects. Peel off the copper wire to see that the color of the contact surface with the base (the so-called rough surface) changes., And the color of ordinary copper foil is different, look at the original copper background color, thick copper foil is peeled off.

2. During the local collision of the PCB circuit board, the copper wire is separated from the substrate by external mechanical force. If the positioning is poor or the direction performance is poor, the copper wire will be obviously deformed, or there will be scratches/impact marks in the same direction.

Peel off the broken copper wire and see the copper foil on the surface of the wool. You can see that the color of the copper foil hair is normal, there will be no lateral erosion, and the peel strength of the copper foil is normal.

3. The PCB circuit board line design is unreasonable, and the fine lines designed with thick copper foil will also cause the line to be etched too much and the copper will be thrown away.

Second, the reason for the lamination process: In general, as long as the hot pressing of the laminate exceeds 30 minutes, the copper foil and the prepreg are basically completely combined, so the compaction will generally not affect the adhesion of the laminated copper foil and the substrate.

However, during the lamination and stacking process, if the PP is contaminated or the copper foil hair is damaged, it will also cause insufficient adhesion between the laminated copper foil and the substrate, resulting in positioning (only for large boards) or sporadic copper wires falling off. However, the measurement of the peel strength of the copper foil close to the circuit will not be abnormal.

3. Reasons for laminate raw materials: 1. The above-mentioned ordinary electrolytic copper foil is a wool foil galvanized or copper-plated product. If the wool foil production peak is abnormal, or galvanized/coppered, the coating is not bad, resulting in the peeling strength of the copper foil itself Not enough, after the circuit board is plug-in, the poor aluminum foil pressed sheet made of PCB will cause the PCB copper wire to fall off due to the impact of external force.

This kind of copper throws out the poorly peeled copper wire to look at the surface of the copper foil wool (that is, the contact surface with the substrate). Lateral erosion will not be obvious, but the peeling strength of the copper foil on the entire surface will be very poor. 2. The adaptability of copper foil and resin is poor: now we use some special performance laminates, such as HTg board, because the resin system is different, the curing agent is generally PN resin, the resin molecular chain structure is simple, and it will be cured when the degree of crosslinking is low. It is necessary to use a special peak copper foil to match it. When the copper foil used in the production of laminates does not match the resin system, the peeling strength of the sheet metal foil is insufficient, and the plug-in will also have poor copper wire shedding.