Standard for evaluating the quality of solder joints in electric soldering irons and the causes of defective solder joints
1. Standard Tin Point
(1) The tin dots form an internal arc.
(2) Tin dots should be round, smooth, without pinholes or rosin stains.
(3) Wire the pins, and the length of the pins should be between 1-1.2MM.
(4) The appearance of the part foot shows good flowability of tin.
(5) Tin surrounds the entire upper tin position and part feet.
2. Determination of non-standard tin points
(1) False soldering: Seemingly soldered but not actually soldered, mainly due to dirty solder pads and pins, or insufficient soldering flux and heating time.
(2) Short circuit: A component with feet is short circuited between them due to excess solder, or due to improper operation by inspectors using tweezers, bamboo sticks, etc., resulting in contact short circuits between feet. This also includes residual tin slag causing short circuits between feet.
(3) Deviation: Due to inaccurate positioning of the device before welding or errors caused during welding, the pins are not within the specified solder pad area.
(4) Low tin: Low tin refers to the tin point being too thin to fully cover the copper sheet of the part, which affects the connection and fixation effect.
(5) Excessive tin: The part feet are completely covered with tin and form an outer arc, making the appearance and solder pad position of the part invisible, and it cannot be determined whether the part and solder pad are well soldered.
(6) Wrong parts: If the specifications or types of parts placed do not comply with the operation regulations or BOM or ECN, it is considered a wrong part.
(7) Missing parts: The position where parts should be placed, resulting in gaps due to abnormal reasons.
(8) Tin balls and slag: Excess solder balls and slag attached to the surface of the PCB board can cause small pin short circuits.
(9) Polarity reversal: If the polarity orientation accuracy is inconsistent with the processing requirements, it is considered a polarity error.
3. Causes of poor solder joints
(1) Forming tin balls, tin cannot spread throughout the entire solder pad
The temperature of the soldering iron is too low, or the soldering iron head is too small; Solder pad oxidation.
(2) Forming a tin tip when removing the soldering iron
The soldering iron is not hot enough, and the soldering flux has not melted, which will take effect step by step. The temperature of the soldering iron head is too high, the flux evaporates, and the welding time is too long.
