It is mainly to clean the copper surface by micro-etching. The depth of micro-etching is generally 0.75-1.0 microns. At the same time, the attached organic pollutants are removed, so that the copper surface is really clean, and it can effectively contact with molten tin, and quickly generate IMC. The uniformity of micro-etching will make the copper surface have good solderability; after washing with water, it will be quickly dried by hot air.
The preheating zone is generally an infrared heating tube with a length of about 1.2 meters or 4 feet up and down. The speed of the board transmission depends on the size, thickness and complexity of the board. The speed of the ’60mil (1.5mm) board is generally 4.6-9.0m/min. When the PCB board surface temperature reaches 130-160 degrees, flux coating, double-sided coating, can use hydrochloric acid as the activated flux; preheating before flux coating can effectively prevent the metal in the preheating section Parts will not rust or burn out due to dripping flux.
The tin content in the tin melting tank is about 430 kg, which is a solder alloy composed of 63/37 eutectic, and the temperature is maintained at about 260 degrees. The tin-melting instant noodles are intentionally floated with a layer of ethylene glycol oil, which should be considered compatible with the flux. The rolling transfer speed of the board is about 9.1m/min through the transfer wheel, and there are three rows in the tin furnace area. For the upper and lower rollers, the dwell time is only about 2 seconds. The span between the front and rear groups of rollers is 6 inches, and the length of the rollers is more than 24 inches, so the upper limit of the board surface that can be processed is 24 inches. The spacing between them is 15-30mil, and the air knife is inclined at 2-5 degrees to the vertical moon, which is conducive to blowing off the tin in the hole and the tin pile on the board surface.
Board thickness, pad spacing, pad shape, tin thickness (The distance between them is quite wide, so it is easy to cause unevenness of the tin surface of the pad).
First, use cold air to blow from bottom to top on the air bed of about 1.8 meters, then float the board surface, cool the lower surface first, and continue to blow cold air from top to bottom in the runner bearing area of about 1.2 meters. The cleaning process removes flux residue without causing too much thermal shock.
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