Standards for evaluating the quality of soldering iron solder joints, the causes of bad solder joints
(1) The tin point is in an inner arc.
(2) The tin spot should be round, smooth, free of pinholes and rosin stains.
(3) There must be stitches, and the length of the stitches should be between 1-1.2MM.
(4) The appearance of the part feet shows that the tin has good fluidity.
(5) Tin surrounds the entire upper tin position and parts feet.
2. Judgment of non-standard tin points
(1) False soldering: It seems that the soldering is actually not soldered, mainly because the pads and pins are dirty or the flux and heating time are not enough.
(2) Short circuit: parts with feet are short-circuited by excess solder between the feet, or short-circuited due to improper operation of inspectors using tweezers, bamboo sticks, etc. Short circuit with pin.
(3) Offset: due to inaccurate positioning of the device before welding, or mistakes made during welding, the pins are not within the specified pad area.
(4) Less tin: Less tin means that the tin point is too thin to fully cover the copper skin of the part, which affects the connection and fixing effect.
(5) Too much tin: The part feet are completely covered by tin and form an outer arc, so that the shape of the part and the pad position cannot be seen, and it is impossible to determine whether the parts and pads are tinned well.
(6) Wrong parts: If the specifications or types of parts placed do not match the operation regulations or BOM and ECN, they are wrong parts.
(7) Missing parts: The position where the parts should be placed is vacant due to abnormal reasons.
(8) Solder balls and tin slag: Excess solder balls and tin slag attached to the surface of the PCB will cause small pins to short circuit.
(9) Polarity reversal: The correctness of the polarity orientation is inconsistent with the processing requirements, that is, the polarity is wrong.
3. Causes of bad solder joints
(1) Solder balls are formed, and tin cannot 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 pad is oxidized.
(2) Tin tip is formed when the soldering iron is removed
The soldering iron is not hot enough, the flux is not melted, and the steps work. If the temperature of the soldering iron tip is too high, the flux will evaporate and the soldering time will be too long.
