PCBA Tech - Six precautions before SMT patch resistance is used

It is well known to all in the industry that in SMT patch processing, the detection and selection of patch resistance is a crucial link. Smt patch resistance is one of the most common electronic components in the SMT patch processing industry. However, some patch resistors are encapsulated in a small size, which makes it easy to confuse patch resistors during use.

Next, SMT technicians from IPCB will briefly introduce some precautions before using patch resistors.

(1) When SMT technical operator of PCBA manufacturer works, the multimeter is used to measure the patch resistance. At this time, the power supply in the circuit should be disconnected, one end of the patch resistance should be disconnected from the circuit, avoiding the formation of parallel connection with other circuit elements, which will affect the accuracy of the measurement value. Smt technicians cannot use both hands to touch both ends of the meter at the same time when measuring resistance, which will form a parallel connection between patch resistance and human resistance, which will affect the accuracy of measurement values. If you need to measure the patch resistance with high precision, you need to use a resistance bridge to measure it.

(2) Smt technicians use a multi-meter to measure resistance before using it. They can only use it after checking it correctly. The patch resistance with the text mark ensures that the marked side is facing upward when mounting, for easy post-inspection.

(3) Potentiometers are prone to noise and other faults after use, and the probability of unpacked potentiometers with switches is higher. The contact resistance is unstable mainly due to the damage of the resistance film. If the case is mild, alcohol can be used to clean the resistance film to effectively remove the dirt and toner produced by friction. If serious, consider replacing the potentiometer.

(4) Selection of rated power and high power patch resistance will increase the cost of volume increase, which is not conducive to circuit design. Also, the power can not be too small, which will affect the normal use of the circuit; Generally, the value of rated power is twice the actual power.

(5) Selection of error size, patch resistance selection is generally (+) 10% of the value of the circuit diagram, where the individual precision requirements are high, can be marked separately.

(6) Due to the large use of small and ultra-small resistors in electronic devices, relevant SMT technicians need to use thin and sharp soldering heads with power below 30W during welding operations; Do not cut the lead too short to avoid heat transfer into the resistance during welding, which may cause errors.