Assemble USB circuit board

by:A-TECH      2020-04-24
Circuit board circuit board it is more common in our daily life, electronic and electrical products, but its products are different in size and size, generally speaking, it is divided into three categories: single-panel, double-panel and multi-layer. Multi-layer PCB boards are now produced by a large number of manufacturers. The good and the bad are mixed. Impurities, dust, Rosin and solder will inevitably be produced on the surface of the circuit board during the production process. We must clean the circuit board before leaving the factory, otherwise, it will affect the quality and reputation of our factory. Then the question is, in the face of the production of thousands of circuit boards, such a large number, how to clean the circuit board is clean? In the past, my standard cleaning method was to use 99% isopropanol ordinary cotton swabs. It can dissolve flux residues, but this kind of cotton swab easily stumbles on the sharp corners of the parts, quickly becomes fragments, and leaves fine cotton fibers anywhere. Behind the use of the Meidi sponge cotton swabs and cloth cotton swabs, these cotton swabs are basically designed for industrial use. In any case, the packaging and winding of cotton are tighter than that of cotton swabs, and they are 'low Velvet' and show superior wear resistance and cleanliness, which can be wiped repeatedly. It helps to reduce shredding and stray cotton fibers, but it cannot completely eliminate them. As you can see here, isopropyl alcohol also leaves seemingly unattractive residues. Its visibility depends to a large extent on the angle of light. I deliberately chose the worst angle photo. I am not sure whether this kind of residue really comes from alcohol or whether it dissolves in alcohol, but whether there are stripes on the PCB when drying. I found that I needed to wait until it dried, then wipe the dry part with another dry cotton swab and remove the stripes. The final result is still not perfect, although it is very good. However, the whole cleaning process can be very time consuming, and each circuit board takes several minutes. Meidi's microfiber cotton swabs have been used in the back. This cotton swab sponge is more wear-resistant, scratch-resistant and dust-removing. Why should the circuit board after reflow soldering be cleaned? It is very important to clean the circuit board after reflow soldering, because all the welding materials containing more active agents need to be cleaned, so that the wettability and diffusivity of the welding materials will be better, but there will be residues after reflow soldering, the residue will corrode the substrate, so it needs cleaning. Most of the cleaning methods are ultrasonic cleaning, but it may damage the device because the frequency is close to or the same, causing resonance and resonance damage. At present, the crystal oscillator used in the industry has a frequency of several thousand Hz, while the ultrasonic frequency used in the ultrasonic cleaning machine is basically tens of thousands of Hz, with a frequency difference of one order of magnitude, individual crystal oscillators with special frequencies need to be tested to verify whether they will have adverse effects. Despite the residue of cleaning-free flux, there is still a high risk of 'creep current' during use, resulting in product failure. Also, a large part of the PCBA that needs to be cleaned after cleaning-free flux welding is that the product needs to be coated and protected. Experiments show that if the flux residue is not thoroughly cleaned and directly coated, the coating will crack after temperature circulation. The reliability of the product is not as high as that of coating.
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