In SMT processing, solder paste printing, SMT chip, reflow soldering, etc. are all key processing steps, but before processing, there is a very important process is incoming inspection, the following Shenzhen Viasion Electronics introduces the types and methods of inspection before SMT assembly.
Inspection before SMT assembly (incoming inspection)
First, the test method
The inspection methods mainly include visual inspection, automatic optical inspection (AOI), X-ray inspection and ultrasonic inspection, online measurement, and functional testing.
1. Visual inspection refers to the method of verifying the quality of assembly directly with the naked eye or with the aid of tools such as magnifiers and microscopes.
2. Automatic optical inspection (AOI), mainly used for process inspection: solder paste printing quality inspection after printing machine, placement quality inspection after placement, and post-weld inspection after reflow oven, automatic optical inspection is used instead Visual inspection.
3. X-ray inspection and ultrasonic inspection are mainly used for solder joint inspection of BGA, CSP and Flip Chip.
4. The online test equipment uses special isolation technology to test the resistance value of the resistor, the capacitance value of the capacitor, the inductance value of the inductor, the polarity of the device, and the parameters such as short circuit (bridge) and open circuit (open circuit), and automatically diagnose errors. And faults, and can display and print out errors and faults.
5. Functional testing is used for electrical functional testing and inspection of PCBA boards.
The functional test is to input the electrical signal of the measured unit on the PCBA board or the PCBA board as a functional body, and then detect the output signal according to the design requirements of the functional body. Most functional tests have diagnostic programs that can identify and determine faults. However, the equipment for functional testing is more expensive. The simplest functional test is to connect the PCBA board to the corresponding circuit of the device for power-on, to see if the device can run normally. This method is simple and has little investment, but it cannot automatically diagnose the fault.
Which method is used should be determined according to the specific conditions of each unit's SMT production line and the assembly density of the PCBA board.
Second, incoming inspection
Incoming material inspection is the primary condition for ensuring the quality of PCBA processing. The quality of components, printed circuit boards and PCBA processing materials directly affects the assembly quality of PCBA boards. Therefore, the electrical performance parameters of the components and the solderability of the soldering tips and leads; the designability of the printed circuit board and the solderability of the solder pads; solder paste, paste adhesive, rod solder, solder, cleaning agent The quality of PCBA processing materials must have a strict incoming inspection and management system.
Third, PCBA processing components (SMC / SMD) inspection
The main test items of the test components: weldability, pin coplanarity and usability, should be sampled by the inspection department.
As the PCBA processing workshop, the following visual inspections can be performed:
1. Visually or use a magnifying glass to check the solder joints or lead surfaces of the components for oxidation and contamination.
2. The nominal value, specification, model, accuracy, and dimensions of components shall be in accordance with the product process requirements.
3. The pins of SOT and SOIC should not be deformed. For multi-lead devices QFP with lead spacing below 0.65mm, the pin coplanarity should be less than 0.1mm (can be optically detected by the mounter).
4. For products that require cleaning, the marking of the components after cleaning will not fall off, and the performance and reliability of the components will not be affected (visual inspection after cleaning).
Fourth, printed circuit board (PCB) inspection
1. The layout pattern and size of the PCB, the solder mask, the screen, and the vias should be set in accordance with the PCB design requirements. (Example: Check if the pad pitch is reasonable, whether the screen is printed on the pad, whether the via hole is on the pad, etc.).
2. The external dimensions of the PCB should be consistent. The external dimensions, positioning holes, and reference marks of the PCB should meet the requirements of the production line equipment.
3. PCB allows warpage size:
3.1 Up/convex: Maximum 0.2mm/5Omm Length up to 0.5mm / length of the entire PCB.
3.2 Down/Concave: Max. 0.2mm/5Omm Length up to 1.5mm / length of the entire PCB.
4. Check the PCB for contamination or moisture.