Why Did PCB Copper Wire Fall Off


When the copper wire of PCB falls off, all PCB brands will argue that it is a laminate problem and require their production plants to bear bad losses. According to many years of customer complaint handling experience, the common reasons for PCB copper fall off are as follows:


1, PCB factory process factors:


1),Copper foil is over etched.


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). The common copper rejection is generally galvanized copper foil above 70UM. There has been no batch copper rejection for red foil and ashing foil below 18um. When the circuit 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 an active metal, when the copper wire on the PCB is soaked in the etching solution for a long time, it will lead to excessive line side corrosion, resulting in the complete reaction of some thin line backing zinc layers and separation 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 water washing and drying after etching are poor, resulting in that the copper wire is also surrounded by the residual etching solution on the PCB toilet surface. If it is not treated for a long time, it will also produce excessive side corrosion of the copper wire and throw copper.

This situation is generally concentrated on the thin line road or wet weather. Similar defects will appear on the whole PCB. Peel off the copper wire to see that the color of its contact surface with the base layer (i.e. the so-called coarsened surface) has changed, which is different from the color of normal copper foil. What you see is the original copper color of the bottom layer, and the peel strength of copper foil at the thick line is also normal.


2),Local collision occurs in PCB production process, and the copper wire is separated from the substrate by external mechanical force.


There is a problem with the positioning of this poor performance, and the fallen copper wire will have obvious distortion, or scratches or impact marks in the same direction. Peel off the copper wire at the bad part and look at the copper foil rough surface. It can be seen that the color of the copper foil rough surface is normal, there will be no side corrosion, and the stripping strength of the copper foil is normal.


3),PCB circuit design is unreasonable.

Designing too thin lines with thick copper foil will also cause excessive line etching and copper rejection.


2,Laminate process reason:

Under normal circumstances, as long as the hot pressing high-temperature section of the laminate exceeds 30 minutes, the copper foil and the semi cured sheet are basically combined completely, so the pressing generally will not affect the bonding force between the copper foil and the substrate in the laminate. However, in the process of lamination and stacking, if PP is polluted or the rough surface of copper foil is damaged, it will also lead to insufficient bonding force between copper foil and substrate after lamination, resulting in positioning deviation (only for large plates) or sporadic copper wire falling off, but there will be no abnormality in the peel strength of copper foil near the off-line.


3,Laminate raw material reason:


1),As mentioned above, ordinary electrolytic copper foil is galvanized or copper plated products of wool foil. If the peak value of wool foil is abnormal during production, or the coating crystal branches are poor during galvanizing / copper plating, resulting in insufficient peel strength of the copper foil itself. After the bad foil is pressed into PCB, the copper wire will fall off under the impact of external force in the plug-in of the electronic factory. This kind of copper throwing is poor. When the copper wire is stripped, there will be no obvious side corrosion on the rough surface of the copper foil (i.e. the contact surface with the substrate), but the peel strength of the whole copper foil will be very poor.


2),Poor adaptability between copper foil and resin: for some laminates with special properties, such as HTG sheet, due to different resin systems, the curing agent used is generally PN resin. The molecular chain structure of the resin is simple and the cross linking degree is low during curing. It is bound to use copper foil with special peak to match it. When the copper foil used in the production of laminate does not match the resin system, resulting in insufficient peel strength of metal foil coated on the plate, and poor copper wire falling off when inserting.

Post time: Aug-17-2021