Typewriter printed circuit board assembly
Although the copper foil is soft, repeated repeated bending or reciprocating motion or impact is still very likely to cause the fracture to occur. If it is visible to the naked eye, it is easy to solve the problem, because only the position of the fracture is observed. In general, the cause of the fracture can be known, and further countermeasures can be taken.
It is more difficult to measure the open/open circuit from the end of the gold finger, but how can the copper foil break position be found, and it is difficult to confirm the cause of the fracture caused by the position.
First, observe the problem line with a microscope, first find the location of the suspected fracture as a mark. If the microscope can not find any suspicious fracture position, you can also divide the line into several small segments. At both ends of the line where the line may break, or at the position of the segment, carefully cut the cover film of the soft board with a blade, preferably with a new utility knife or engraving knife, then the blade Place it on the outer cover film to move left and right to scrape the cover film and expose it to the underlying copper foil line. This way you can take a three-meter meter to measure the line. Then gradually remove the position where the breakage may occur, and finally find the exact location of the fracture of the copper foil line. If you are worried that this method may break the copper foil line, you can also try to cut the copper foil line without the copper foil, and then try to tear the cover film to achieve the same purpose.
HotBar (hot-rolled tin soldering), its main function is to re-melt the solder paste already printed on the printed circuit board (PCB) by using the thermomodes, so as to connect two separate electronic parts, the most common The result is a soldered flexible cable (FPC) soldered to an electronic printed circuit (PCB).
Since the hot head of the HotBar machine is the only heat source, when the hot head is pressed down on the flexible cable (FPC), the heat must be conducted down to the printed circuit board (PCB) to melt the printed circuit board. Solder paste, but there is a soft line in the middle, so the soft cable should also have a heat transfer function design, in order to achieve the best heat transfer effect and the best quality of solder.
The most common design is to make Plating holes or Vias on the FPCB solder pads as the interface for heat conduction, as shown in the following figure. It is generally recommended to have three Vias or 2.5 Vias on a separate pad for each FPC. There is also a benefit in making electroplated holes on the FPCB. In the hot-weld soldering tin soldering operation, the tin can be spilled through the plating holes without causing a short circuit between the pads; the operator can also check the Vias. The most common design is to make Plating holes or Vias on the FPCB solder pads as the interface for heat conduction, as shown in the following figure. It is generally recommended to have three Vias or 2.5 Vias on a separate pad for each FPC. There is also a benefit in making electroplated holes on the FPCB. In the hot-weld soldering tin soldering operation, the tin can be spilled through the plating holes without causing a short circuit between the pads; the operator can also check the Vias.
In addition, attach a double adhesive to the flexible cable to attach the flexible cable to the circuit board, because the operator is unlikely to hold the FPC until the HotBar is completed, even if it can There will be problems with unstable quality.
To sum up, the design requirements of FPC are as follows. (In addition, the design of electronic products is now more and more oriented towards light and thin. In order to save space, there are more and more designs without plating holes and via holes, and there is time to discuss them separately.)
▪ It is best to have three plating holes or via holes on each FPC pad, and at least two + half plated holes or via holes.
▪ Apply double-sided tape on the side of the flexible cable (FPB) attached to the board. The thickness of the double-sided tape should be less than 0.15mm. The distance from the edge of the FPC pad to the double-sided tape should be 0.20mm. distance.
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