PCB factory process factors
1.The copper foil is over-etched. The electrolytic copper foils used in themarket are generally single-sided galvanized (commonly known as ashing foil)and single-sided copper plating (commonly known as red foil). The common throwncopper is generally more than 70um galvanized copper Foil, red foil and ashfoil below 18um basically have no batch copper rejection.
Whenthe customer circuit design is better than the etching line, if the copper foilspecifications are changed but the etching parameters remain unchanged, theresidence time of the copper foil in the etching solution is too long. Becausezinc is originally a lively metal, when the copper wire on the LED advertisingscreen PCB is immersed in the etching solution for a long time, it will inevitablylead to excessive side corrosion of the circuit, causing some thin circuitbacking zinc layer to be completely reacted and contact with the substrate. Thematerial is detached, that is, the copper wire falls off.
Anothersituation is that there is no problem with the PCB etching parameters, but thecopper wire is also surrounded by the remaining etching solution on the PCBsurface after the etching, and the copper wire is also surrounded by theresidual etching solution on the PCB surface. Throw the copper. This situationis generally manifested as concentrated on thin lines, or during periods of wetweather, similar defects will appear on the entire PCB. Strip the copper wireto see that the color of the contact surface with the base layer (the so-calledroughened surface) has changed. The color of the copper foil is different fromthe normal copper foil. 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.Part of the collision occurred in the PCB process of the LED advertisingscreen, and the copper wire was separated from the base material by externalmechanical force. This poor performance is poor positioning or orientation, thecopper wire will be obviously twisted, or scratches/impact marks in the samedirection. If you peel off the copper wire at the defective part and look atthe rough surface of the copper foil, you can see that the color of the roughsurface of the copper foil is normal, there will be no side erosion, and thepeeling strength of the copper foil is normal.
3.The PCB circuit design of the LED advertising screen is unreasonable. If athick copper foil is used to design a circuit that is too thin, it will alsocause the circuit to be over-etched and the copper will be thrown away.
Second,the reason for the laminate process
Undernormal circumstances, the copper foil and the prepreg will be basicallycompletely bonded as long as the high temperature section of the laminate ishot pressed for more than 30 minutes, so the pressing will generally not affectthe bonding force of the copper foil and the substrate in the laminate.However, in the process of stacking and stacking laminates, if the PP iscontaminated or the matte surface of the copper foil is damaged, it will alsocause insufficient bonding force between the copper foil and the substrateafter lamination, resulting in positioning (only for large plates) Words) orsporadic copper wires fall off, but the peel strength of the copper foil nearthe off-line is not abnormal.
3. Reasons for laminate raw materials
1.It is mentioned on the LED advertising screen that ordinary electrolytic copperfoils are all products that have been galvanized or copper-plated on wool. Ifthe peak value of the wool foil is abnormal during production, or whengalvanizing/copper plating, the plating crystal branches are bad, resulting incopper. The peel strength of the foil itself is not enough. After the bad foilis pressed into a PCB and plug-in in the electronics factory, the copper wirewill fall off due to the impact of external force. This kind of poor copperrejection will not cause obvious side corrosion after peeling the copper wireto see the rough surface of the copper foil (that is, the contact surface withthe substrate), but the peeling strength of the entire copper foil will be verypoor.
2.The poor adaptability of the copper foil of the LED advertising screen to theresin: some laminates with special properties, such as HTg sheets, are used nowbecause of different resin systems, the curing agent used is generally PNresin, and the resin molecular chain structure is simple , The degree ofcross-linking is low during curing, and it is necessary to use copper foil witha special peak to match it. When producing laminates, the use of copper foildoes not match the resin system, resulting in insufficient peeling strength ofthe sheet metal-clad metal foil, and poor copper wire shedding when inserting.
Attachedlink--https://blog.csdn.net/weixin_28706423/article/details/112492648