Turnkey pcb assembly detection categories
1, Turnkey pcb assembly size and appearance inspection
The size inspection of the turnkey pcb assembly is mainly related to the diameter of the hole, the spacing and tolerance, and the edge size of the turnkey pcb assembly. Appearance defect detection mainly includes: solder mask and pad alignment; solder mask film for impurities, peeling, wrinkling and other abnormal conditions; the reference mark is qualified; circuit conductor width (line width) and spacing are consistent to requirements; whether the multilayer board is peeled off, etc. In practical applications, PCB appearance test equipment is often used to detect it. Typical equipment is mainly composed of computer, automatic workbench, image processing system and other parts. This system can detect the inner and outer layers of the multi-layer board, single/double-panel, and base film; it can detect broken lines, wires connection, scratches, pinholes, line widths, edges roughness and large area defects, etc.
Unreasonable design and improper handling of the technics process may cause warpage and distortion of the PCB. The test method is to expose the tested PCB to a thermal environment representative of the assembly technics and perform thermal stress testing. Typical thermal stress testing methods are rotary immersion testing and solder floating testing, in which the PCB is immersed in molten solder for a certain period of time and then removed for warpage and distortion detection.
Manually measuring the turnkey pcb assembly is done by placing the three corners of the PCB against the table and measuring the distance of the fourth corner from the table. This method can only be used for rough estimation, and more effective methods include applying ripple imaging technology. The ripple image method is: placing an inch 100 line grating on the PCB to be tested, and setting a standard light source to be incident on the PCB through the grating at an incident angle of 45 ° C. The raster image is generated on the PCB by the grating, and then a CCD camera is used to look at the raster image directly above the PCB. At this time, geometric interference fringes generated between the two gratings can be seen on the entire PCB. This stripe shows the offset in the Z direction. The number of stripes can be counted to calculate the offset height of the PCB, and then converted warpage degree by calculation. .
2, PCB solderability test
The solderability test of turnkey pcb assembly focuses on the testing of pads and plated through holes. The solderability test method for PCBs is specified in standards such as IPC-S-804. It includes edge immersion test, rotary immersion test, and wave immersion test. And solder beads testing, etc.
3, PCB solder mask integrity test
A dry film solder mask and an optical imaging solder mask are generally used on the pcb, and the two solder masks have high resolution and non-flowing character. Dry film solder mask is laminated to the PCB under pressure and heat, which requires a clean PCB surface and an effective lamination technics. The surface of the solder mask tin-lead alloy has poor adhesion, and under the thermal stress of reflow soldering, peeling and cracking from the surface of the PCB often occurs. The solder mask is also brittle, and micro-cracks may occur due to heat and mechanical forces during leveling. In addition, physical and chemical damage may occur due to the action of the cleaning agent. In order to find out the potential defects of the dry film solder mask, the PCB should be proceed a rigorous thermal stress test in the incoming inspection. When the solder mask peeling phenomenon was not observed during the test, the tested PCB was immersed in water after the test, and the peeling phenomenon of the solder mask was observed by capillary action between the solder resist film and the surface of the PCB. The PCB test piece can also be immersed in the SMA cleaning agent after the test to observe whether it has physical and chemical effects with the solvent.
4, PCB internal defect detection
Micro-slice technology is generally used to detect internal defects of PCB. The specific detection methods are clearly defined in IPC-TM-650 and other related standards. The main inspection items for microslice inspection include the thickness of copper and tin-lead alloy plating, the alignment of the inner conductor layers of the multilayer board, lamination voids and copper cracks.
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