printed circuit board is one of the indispensable components of electronIC equipment, it appears in almost every kind of electronic equipment, in addition to fixing a variety of large and SMAll parts, the main function of printed circuit board is to make various parts electrical connection. The abnormal quality of PCB board will cause direct losses to customers and PCB manufacturers. The loss of copper wire is one of the abnormal quality phenomena, but the loss to PCB manufacturers is greater. The loss of copper wire, as the name implies, means that the wire falls off from the FR4 substrate. So what are the reasons for the copper wire to fall off?
Reasons for laminate raw materials:
Under normal circumstances, as long as the hot pressing high temperature section of laminate more than 30 minutes, copper foil and sEMI-cured sheet is basically combined completely, so pressing generally will not affect the binding force of copper foil and substrate in laminate. However, in the process of laminate stacking and stacking, if PP pollution or copper foil surface damage, it will also lead to insufficient bonding force between copper foil and substrate after laminate, resulting in positioning (only for the large plate) or sporadic copper wire loss, but the stripping strength of copper foil near the stripping line will not be abnormal.
Ordinary electrolytic copper foil is galvanized or copper-plated products. If the peak value of wool foil production is abnormal, or galvanized/copper-plated, the coating crystal dendrite is bad, resulting in the peeling strength of copper foil itself is not enough. After the bad foil is pressed into printed circuit board, the copper wire will fall off under the impact of external force when SMT plug-in. This kind of bad stripping copper wire copper foil surface (i.e. contact surface with the substrate) will not be obvious side erosion, but the whole surface of copper foil peeling strength will be very poor.
Poor adaptability of copper foil and resin
Some laminates with special properties are used now, such as HTg sheet, because the resin system is not the same, the curing agent is generally PN resin, resin molecular chain structure is SIMple, the degree of crosslinking is low when curing, it is bound to use special peak copper foil to match with it. When the production of laminate using copper foil and the resin system does not match, resulting in sheet metal foil peeling strength is not enough, plug-in will also appear bad copper wire shedding.
Excessive etching of copper foil
Electrolytic copper foil used on the MARKet is generally single-side galvanized (commonly known as gray foil) and single-side plated copper (commonly known as red foil), the common copper is generally more than 70um galvanized copper foil, red foil and 18um below the basic ash foil has not been a batch of copper. When the customer line design is better than the etching line, if the copper foil specifications are changed and the etching parameters are not changed, the residence time of copper foil in the etching liquid is too long. Because zinc is active metal, when the copper wire on PCB board is soaked in etching liquid for a long time, it will lead to excessive side erosion of the line, resulting in some fine line backing zinc layer is completely reacted off and separated from the substrate, that is, the copper wire falls off.
The adaptability of copper foil and resin is poor. When the copper foil is used in the production of laminate, it does not match the resin system, resulting in insufficient peeling strength of sheet metal foil, and poor shedding of copper wire will occur in PCB processing. PCB processing process in the local collision, copper wire by external mechanical force and away from the substrate. Falling copper wire will have noticeable twisting, or scratches/impact marks in the same direction. Peel off the bad part of the copper wire to see the copper foil surface, you can see the normal color of the copper foil surface, there will be no bad side erosion, copper foil peeling strength is normal.
There is also a situation that PCB etching parameters have no problem, but after etching washing, and poor drying, resulting in copper wire is also in PCB surface residual etching liquid surrounded, a long time without treatment, will also produce excessive copper wire side erosion and copper. This situation is generally manifested as concentrated on the fine line, or in the wet weather period, the whole PCB circuit board will appear similar bad, strip the copper wire to see its contact surface with the base (namely, the so-calLED coarse surface) color has changed, and the normal copper foil color is not the same, see is the bottom of the original copper color, thick line copper foil peeling strength is normal.
The circuit design is not reasonable
The design of too thin line with thick copper foil will cause excessive etching of line and copper throwing. Copper foil etching is excessive, electrolytic copper foil used on the market is generally single-side galvanized and single-side copper plating, the common copper is generally more than 70um galvanized copper foil, red foil and below 18um ash foil basically have not appeared batch copper.