PCBA Tech - Notice PCBA circuit board production process flow

Today's SMT manufacturing is basically automated machines. The blank board (PCB) is placed at the front end of the SMT production line, and the PCBA assembly line is completed at the end, all done on the same production line.

1. Empty board loading (automatic board loading machine)

The first step of assembling the circuit board is to arrange the empty boards (pcb) neatly, and then put them on the material rack. The automatic board loading machine will automatically send the boards one by one to the printing machine of the SMT assembly line through the docking station.

2. Printing solder paste (solder paste printer)

The first step for the printed circuit board to enter the SMT production line is to print solder paste, which will be printed on the solder pads of the components to be soldered on the PCB. These solder pastes will melt and remove the electronic components when they are subjected to high-temperature reflow soldering. Solder on the circuit board.

3. Solder Paste Inspection Machine (SPI)

The quality of solder paste printing (more tin, less tin, whether the solder paste is sticky, etc.) is related to the quality of the soldering of the subsequent components. Therefore, some SMT factories will use optical instruments to check the tin after the solder paste is printed in order to ensure the stability of the quality. The quality of the paste printing, if there is a poorly printed board, knock it off, wash off the solder paste on it and reprint it, or use a repair method to remove the excess solder paste.

4. High-speed placement machine

The high-speed placement machine will first place some small electronic components (such as small resistors, capacitors, inductors) 0201,0402 and other components on the circuit board. These parts will be slightly stuck by the solder paste that has just been printed on the circuit board. So the mounting speed is very fast, and the components on the board will not fly away, but large electronic components are not suitable for high-speed machine mounting, which will drag down the rapid speed of small parts.

5. General Mounter/Multifunctional Mounter

The placement machine is not used to paste some relatively large electronic components, such as BGA, IC, connector, SOP, etc. These components need to be accurately positioned, and the alignment is very important. Before the placement, the camera will be used to confirm the parts. Location, so the speed is relatively slow. Because of the size of the components, there may not always be tape-and-reel packaging. Some may be trays (Tray) or tube packaging. If you want the SMT machine to eat pallets or tubular packaging materials, an additional machine must be configured. Therefore, the top of these electronic parts must have a flat surface for the nozzle of the printer to suck the parts, but some electronic components do not have a flat surface for these machines. At this time, you need to customize special nozzles for these machines. For special-shaped parts, either add a layer of flat tape on the part, or wear a flat cap.

6. Reflow soldering

Reflow soldering melts the solder paste on the part feet and the circuit board. The curve of temperature rise and fall affects the quality of the entire circuit board soldering. The general reflow furnace will set the preheating zone, wetting zone, reflow zone, and cooling. Zone to achieve the best soldering effect. The highest temperature in the reflow furnace is best not to exceed 250°C, otherwise there will be many parts deformed or melted because they cannot withstand such a high temperature.

7. Optical inspection machine AOI

Not every SMT production line has an optical inspection machine (AOI). The purpose of AOI is to check whether the parts have tombstones or side standing, missing parts, displacement, bridges, empty soldering, etc., but the solder under the components cannot be judged. False welding, BGA weldability, resistance value, capacitance value, inductance value and other parts quality, so so far there is no way to completely replace ICT. Therefore, if only AOI is used to replace ICT, there are still some risks in terms of quality.

8. Visual inspection of finished products

Regardless of whether there is an AOI process, the general SMT line will still set up a visual inspection area to check whether there are any defects after the circuit board is assembled. If there is an AOI, the number of visual inspection personnel can be reduced, because it is still necessary to check Some places that AOI cannot detect.

9. Circuit board open/short test

The main purpose of the ICT setting of the circuit board open/short test is to test whether the parts and circuits on the circuit board are open or short. In addition, it can also measure the basic characteristics of most parts, such as resistance, capacitance, and inductance, to judge these Whether the function of the parts is damaged, wrong parts, missing parts... etc. after passing through the high temperature reflow furnace.

10. Board cutting machine

General circuit boards will be joined to increase the efficiency of SMT production. There are usually several-in-one boards, such as two-in-one, four-in-one...etc. After all the assembly work is completed, it must be cut into single boards. Some circuit boards with only single boards also need to cut off some extra board edges.