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PCB Tech
Why does the PCB drop the pad and what is the reason?
PCB Tech
Why does the PCB drop the pad and what is the reason?

Why does the PCB drop the pad and what is the reason?

2021-11-08
View:32
Author:Downs

PCB circuit board 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.

2. A collision occurs locally in the PCB process, and the copper wire is separated from the substrate 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. 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.

pcb board

Reasons for the laminate process

Under normal circumstances, the copper foil and the prepreg will be basically completely bonded 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 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.

Reasons for laminate raw materials

1. Ordinary electrolytic copper foil is a product that has been galvanized or copper-plated on the wool foil. If the peak value is abnormal during the production of the wool foil, or when galvanizing/copper plating, the plating crystal branches are poor, resulting in insufficient peel strength of the copper foil itself. , The copper wire will fall off due to the impact of external force when the defective foil pressed sheet material is made into PCB and plug-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 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 cross-linking is low, and a copper foil with a special peak should be used 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.

In addition, it is possible that improper soldering on the client side causes the pad to fall off (especially single and double panels, multi-layer boards have a large area of ground, fast heat dissipation, high temperature required during soldering, and it is not so easy to fall off)

Repeatedly soldering a point will solder off the PCB pad;

The high temperature of the soldering iron is easy to solder off the PCB pad;

If the soldering iron tip exerts too much pressure on the pad and the soldering time is too long, the PCB pad will be soldered off.