In PCB assembly
and processing, PCB will be inspected and tested before processing to select PCB meeting SMT production requirements, and unqualified PCB will be returned to PCB manufacturer
. Specific requirements of PCB can refer to IPC-A-610C international general assembly standard of electronic industry. The following are some basic requirements of small-scale SMT assembly processing for PCB.
1. PCB must be flat and smooth
PCB generally requires that the surface should be flat and smooth, and should not be warped up. Otherwise, when solder paste is printed and assembled, it will cause great harm, such as cracks.
2. Thermal conductivity
In reflow soldering and wave soldering, there will be a preheating area. Generally, the PCB should be heated evenly and reach a certain temperature. The better the thermal conductivity of PCB is, the less defects will be produced.
3. Heat resistance
With the development of SMT process and the requirements of environmental protection, lead-free process has been widely used, which also causes the increase of welding temperature, which puts forward higher requirements for the heat resistance of PCB. When reflow soldering, the temperature of lead-free process should reach 217 ~ 245 ℃ and last for 30 ~ 65s. Therefore, the heat resistance of general PCB should reach 260 ?? and last for 10s.
4. Adhesion of copper foil
The bonding strength of copper foil should reach 1.5kg/cm to prevent PCB from falling off due to external force.
5. Bending standard
PCB has a certain bending standard, generally more than 25kg / mm.
6. Good conductivity
PCB as the carrier of electronic components, to achieve the link between components, we must rely on the circuit of PCB. PCB should not only have good conductivity, but also the broken circuit of PCB can not be directly added, otherwise it will have a great impact on the performance of the whole product.
7. Can withstand solvent washing
PCB in the production, easy to get dirty, often need cleaning solvent and other solvents for cleaning, so, PCB should be able to withstand the solvent washing, and do not produce bubbles and other adverse reactions.
The above are some basic requirements for a qualified PCB during PCB assembly and processing. Of course, there are other requirements, which will not be introduced here.