PCB Technical - Flexible board production of rigid-flex board

Flexible board production of rigid-flex board

The copper wire of the PCB circuit board is bad (also commonly referred to as the copper rejection). PCB factories all say that it is the problem of the laminate and requires their production factories to bear the bad losses.

One, PCB 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 plating (commonly known as red foil). Commonly thrown copper is generally galvanized copper above 70um. Foil, red foil and ash foil below 18um basically have no batch copper rejection.

When the customer line design is better than the etching line, if the copper foil specifications are changed and the etching parameters remain unchanged, the residence time of the copper foil in the etching solution is too long. Because zinc is originally an active metal, when the copper wire on the PCB is immersed in the etching solution for a long time, it will inevitably lead to 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 the etching parameters of the PCB circuit board are not problematic, but after etching, the copper wire is also surrounded by the residual etching solution on the PCB surface, and the copper wire will also be produced if it is not processed for a long time. Excessive undercutting and dumping of copper. This situation is generally manifested as concentrated on thin circuits, or during periods of wet weather, similar defects will appear on the entire PCB circuit board. Strip the copper wire to see that the color of the contact surface with the base layer (the so-called roughened surface) has been changed. The change is different from the normal copper foil color. What you see is the original copper color of the bottom layer, and the peeling strength of the copper foil at the thick line is also normal.

2. A local collision occurred in the PCB circuit board process, and the copper wire was separated from the base material by external mechanical force. This poor performance is poor positioning or orientation, the copper wire will be obviously twisted, or scratches/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.

3, PCB circuit board 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.

2. Reasons for laminate manufacturing process:

Under normal circumstances, as long as the 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 the PP is contaminated or the matte surface of the copper foil is damaged, the bonding force between the copper foil and the substrate after lamination will also be insufficient, resulting in positioning (only for large plates) Words) or sporadic copper wires fall off, but the peel strength of the copper foil near the off-line is not abnormal.

3. Reasons for laminate raw materials:

1. As mentioned above, ordinary electrolytic copper foils are all products that have been galvanized or copper-plated on wool. If the peak value of the wool foil is abnormal during production, or when galvanizing/copper plating, the plating crystal branches are bad, which will cause 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 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.

There are four reasons why the PCB board is dumped copper.

PCB is one of the indispensable parts of electronic equipment. It appears in almost every kind of electronic equipment. In addition to fixing various large and small parts, the main function of PCB is to electrically connect various parts. Because the raw material of the PCB board is a copper clad laminate, there will be a phenomenon of copper rejection during the PCB production process, so what are the reasons for the PCB board rejection?

1. The PCB circuit design is unreasonable, and the thick copper foil is used to design the thin circuit, which will also cause the circuit to be over-etched and the copper will be thrown away.

2. 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 plating (commonly known as red foil). Commonly thrown copper is generally galvanized copper above 70um. Foil, red foil and ash foil below 18um basically have no batch copper rejection.

3. A local collision occurred in the PCB process, and the copper wire was separated from the base material by external mechanical force. This poor performance is poor positioning or orientation, the copper wire will be obviously twisted, or scratches/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.

4. Under normal circumstances, as long as the laminate is hot pressed for more than 30 minutes at a high temperature, the copper foil and the prepreg are basically completely combined, 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, the bonding force between the copper foil and the substrate after lamination will also be insufficient, resulting in positioning (only for large plates) Words) or sporadic copper wires fall off, but the peel strength of the copper foil near the off-line is not abnormal.