In the SMT process, it needs the help of SMT stencil to make fixture aided processing in some cases, such as in the case of the board is very thin (less than 0.8mm),easy to bend and hard to fix, unstable to brush paste and patch, easy to lose electronics parts etc; Before processing, to evaluate the process route according to the board design plan at first, and then to assess whether the need for fixture on the basis of every process.
Before processing, first of all, according to the design plan of the board to evaluate the process route, and then according to the process to assess whether the need for fixture .The fixtures generally include as following:
1、 Re-flow Soldering Carrier
The main material of re-flow soldering carrier is synthetic stone, which is mainly used to locate PCB in the process of printing, pasting and re-flowing of PCB in the SMT manufacturing. In the manufacturing process of the re-flow soldering carrier, it is necessary to ensure that the bearing side of the carrier is greater than or equal to the width of the belt on the track,generally 5mm and above, the thickness of the bearing edge should not be too thick,generally 1.5mm ~2mm
2、 Wave Soldering Carrier
The main material of wave soldering carrier is synthetic stone, which is mainly used to carry the PCB wave soldering,making DIP parts with Tin and then welding. The bearing edge width of wave soldering carrier is designed according to the wave soldering tin claw, usually 5mm or above, and the structure parts cannot be put on the top of bearing side to avoid the interference of tin claw, the thickness of bearing edge should not be too thick, usually 2mm.
3、 Aluminum Alloy Carrier, Magnetic Carrier, Silica Gel Carrier
The main material of above three carriers is synthetic stone, which is mainly used to locate PCB in the process of printing , pasting and re-flowing of PCB in the PCB manufacturing. It is must to select good aluminum alloy material to produce these three carriers, otherwise the carrier will deform when heated and cannot be corrected.