What inspections are needed for PCB manufacturing incoming materials
Time:2020-11-25
Views:16
1. PCB size and appearance inspection
The PCB size test mainly includes the diameter, spacing and tolerance of the machining holes and the small size of the PCB edge. Appearance defect inspection mainly includes solder mask and pad alignment, whether there are impurities in the solder mask, peeling and wrinkles and other abnormal conditions, the reference mark is qualified, the width (line width) and spacing of the circuit conductors meet the requirements, multi-layer Whether there are residual layers on the board, PCB appearance testing equipment is often used for testing in practical applications. Mainly composed of computer, automatic workbench image processing system, etc. The system can detect multiple panels, the inner and outer layers of single/double panels, and check the primer film, and can detect fold lines, delaminations, scratches, pinholes, and lines Wide, line spacing, rough edges and large area defects.
2. PCB warpage and deformation detection
Unreasonable design and incorrect handling may cause PCB warpage. The test method is specified in ipc-tm650 and other standards. The test principle is as follows: the tested PCB is exposed to a representative thermal environment during the assembly process, and a thermal stress test is performed. Typical thermal stress test methods are rotary immersion test and solder float test. In this test method, the immersed PCB must stay in the molten solder for a period of time, and then remove it for warpage and deformation testing. The manual method for measuring PCB warpage is to make the PCB close to the desktop at three angles, and then measure the distance between the fourth angle and the desktop. This method can only be used for rough estimation, there are more effective methods, such as ripple photography. The waveform image method is: place 100 lines of light per inch on the tested PCB, and set a standard light source at an angle of 45" above the PCB. The light will generate the luminous image on the PCB, and then use the CCD The afterimage of the luminous image observed by the camera is just above the PCB (0"). At this point, you can see the interference stripes between the two awnings on the entire PCB. This stripe shows the offset in the z-axis direction. Count the number of stripes to calculate the offset height of the PCB, and then convert it to warpage by calculation.
3, PCB solder mask integrity test
In the SMT process, the PCB usually uses a dry solder mask and an optical imaging solder mask, which has high resolution and stability. The dry solder mask is laminated on the PCB under pressure and heat. It requires a clean PCB surface and an effective lamination process, and the viscosity of the tin-lead alloy surface is very poor. Under the action of thermal stress, peeling and fracture caused by reflow soldering start from the surface of the PCB. This kind of solder mask is also very brittle. In addition, physical and chemical damage may occur under the action of cleaning agents. In order to prevent these potential defects of dry solder mask, the PCB should be subjected to strict thermal stress testing and inspection. This detection mostly uses the solder float test, the time is about 10-15, and the solder temperature is about 260-288°C. No peeling of the solder mask was observed in the test. The PCB sample can be immersed in water after the test, and the peeling phenomenon can be observed by the capillary action of the water between the solder mask and the PCB surface. The PCB sample can also be removed after the test. Immerse in the solvent for observation in SMA cleaner.
4. PCB solderability test
The focus of PCB solderability testing is pad and through-hole plating. Ipcs-804 and other standards specify PCB solderability test methods, including edge immersion test, rotary immersion test and solder bead test. Edge immersion test is used to test the solderability of surface conductors. Rotary immersion test and wave test are used to test the solderability of surface conductors and electrical vias respectively, while the solder bead test is only used to test the solderability of electrical vias. .
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