Evaluation standards for soldering iron solder joint quality and causes of defective solder joints
1. Standard tin points
(1) The tin point is in an inner arc shape.
(2) The tin points should be round, smooth, without pinholes or rosin stains.
(3) There must be wire pins, and the length of the wire pins must be between 1-1.2MM.
(4) The shape of the part's legs shows that the tin has good fluidity.
(5) Tin surrounds the entire upper tin position and part feet.
2. Determination of non-standard tin points
(1) False soldering: It seems that the soldering is actually not done, mainly because the pads and pins are dirty or the flux and heating time are insufficient.
(2) Short circuit: The parts with legs are short-circuited by excess solder between the legs, or the legs are short-circuited due to improper operation by inspectors using tweezers, bamboo sticks, etc., including residual tin slag that causes the legs to short-circuit. Short circuit with the pin.
(3) Offset: Due to inaccurate positioning of the device before welding, or errors during welding, the pins are not within the specified pad area.
(4) Less tin: Less tin means that the tin point is too thin and cannot fully cover the copper skin of the part, affecting the connection and fixing effect.
(5) Excessive tin: The feet of the part are completely covered with tin and form an outer arc shape, so that the shape of the part and the position of the soldering pad cannot be seen, and it is impossible to determine whether the part and the soldering pad are well tinned.
(6) Wrong parts: If the specifications or types of parts placed do not match the job regulations or BOM and ECN, they are considered wrong parts.
(7) Missing parts: The location where parts should be placed is vacant due to abnormal reasons.
(8) Tin balls and tin slag: Excess solder balls and tin slag attached to the surface of the PCB board can cause short circuits on small pins.
(9) Polarity reversal: The correctness of the polarity orientation is inconsistent with the processing requirements, which is the polarity error.
3. Causes of bad solder joints
(1) Tin balls are formed and tin cannot be spread to the entire pad
The temperature of the soldering iron is too low, or the tip of the soldering iron is too small; the soldering pad is oxidized.
(2) A tin tip is formed when the soldering iron is removed
The soldering iron is not hot enough, the flux does not melt, and it does not work. The temperature of the soldering iron tip is too high, the flux evaporates, and the soldering time is too long.
