PCB Tech - Analysis of common causes of PCB dumping copper

Analysis of common causes of PCB dumping copper

The copper wire of the PCB falls off (that is, it is often said that the copper is dumped), and all PCB brands will say that it is a problem with the laminate, and require their circuit board production and processing plants to bear bad losses. Based on years of experience in handling customer complaints, the editor of the PCB electronics factory will understand with everyone that the common reasons for PCB dumping are as follows:

One, circuit board factory 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 red foil). Common copper foils are generally galvanized copper foil over 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 cause the copper foil to stay in the etching solution for 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 circuit, causing some thin circuit 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 side etching of the copper wire. 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 that of normal copper. 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 line is also normal.

2. The PCB circuit design is unreasonable.

Using thick copper foil to design a circuit that is too thin will also cause excessive etching of the circuit and dumping of copper.

3. 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 the positioning, and the copper wire will be obviously twisted, or scratches or impact marks in the same direction. If you 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 side erosion, and the peeling strength of the copper foil is normal.

2. The reason for the laminate process of the circuit board factory:

Under normal circumstances, as long as the circuit board laminate is hot pressed for more than 30 minutes, the copper foil and the prepreg will be basically completely combined, so the pressing will generally 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 contamination or copper foil rough surface damage, it will also lead to insufficient bonding force between the copper foil and the substrate after lamination, resulting in positioning deviation (only for large plates) ) Or sporadic copper wires fall off, but the peeling strength of the copper foil near the off wires will not be abnormal.

Three, the reason for the laminate raw materials of the circuit board factory:

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. After the bad foil pressed sheet material is made into a PCB, the copper wire will fall off when it is impacted by an external force when it is plugged 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 peeling 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 currently used. 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 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 during plug-in.