With the development of science and technology, technical requirements, and now more and more circuit board using surface mount components, compared with the traditional package, it can reduce the area of the circuit board, easy batch processing, high density wiring. The chip inductance of chip resistor and capacitor is greatly reduced, and it has great advantages in high frequency circuit. The inconvenience of surface mount components is not convenient for manual welding. To this end, the circuit board welding engineer takes the common PQFP packaging chip as an example to introduce the basic welding method of surface mount components.

First, the necessary tools and materials
Welding tools need to have 25W copper head, small iron, Jinqiao welding rod, conditional can use the temperature can be adjusted with ESD protection of the welding table, note the iron tip to fine, the top of the width can not be greater than 1mm. A pointed tweezers can be used to move and fix chips and check circuits. Also prepare fine wire and flux, isopropyl alcohol and so on. The purpose of using flux is to increase the fluidity of solder so that the solder can be drawn by iron and wrapped smoothly on the pins and pads depending on the surface tension. Remove the flux from the plate with alcohol after welding.

Two 、 welding method
1, the circuit board welding engineers remind readers in welding before the pads coated with flux, again with iron, so as to avoid the adverse pad tin or oxidized, resulting in bad welding, chips generally do not need treatment.
2. Carefully put the PQFP chip on the PCB board with the tweezers. Be careful not to damage the pins. Align it with the pads and make sure the chips are in the right direction. The iron temperature to more than 300 degrees Celsius, the iron tip with a small amount of solder, use tools have been holding down the alignment position of the chip, plus a small amount of flux in the two diagonal position of the pin, still holding down the chip, welding the two diagonal position of the pin, the chip is fixed and can not move. Re check the position of the chip after welding diagonally. If necessary, adjust or remove and re position on the PCB board.
3. When soldering all the pins, solder the solder on the tip of the iron and apply all the pins to the solder so that the pins remain moist. Contact the end of each pin of the chip with the tip of the soldering iron until the solder flow pin is seen. When soldering, keep the iron tip parallel to the soldered pin to prevent overlap due to excessive soldering.
4. After soldering all the pins, soak all the pins with solder to clean the solder. Remove excess solder wherever necessary to eliminate any short circuit and lap joint. Finally, check whether the tweezers weld, after the completion of the examination, removal of flux from the circuit board, the hard brush dipped in alcohol along the direction of pin carefully wipe, until the flux disappeared.
5, the circuit board welding engineer to remind you of patch resistor is relatively easy to weld, can be the first in a little tin solder, then put a head element, with tweezers element, after welding on the head, and then see if put; if it is placed, and then welded on another head. It takes a lot of practice to really master welding skills.