- Dec 02, 2017 -
The PCB engineer analyzes the welding technique skills
With the development of science and technology, technical requirements, now more and more PCB with SMT components, compared with the traditional packaging, it can reduce the area of the circuit board, easy to do mass production, the high density of wiring. The inductance of patch resistance and capacitance is greatly reduced, which is of great advantage in high frequency circuit. The inconvenience of SMT components is not convenient for manual welding. For this reason, PCB welding engineers take the common PQFP packaging chip as an example to introduce the basic welding method of SMT components.
1. The required tools and materials
Welding tools need to have 25W copper head small soldering iron, gold bridge welding rod, If conditions are available the welding table with ESD protection can be accommodated with temperature, note that the tip of the solder is thin, and the width of the top can't be greater than 1mm. A pointed pair of tweezers can be used to move and fix chips and check circuits. Also prepare fine wire and flux, isopropyl alcohol, etc. The purpose of the use of the flux is to increase the fluidity of the solder so that solder can be drawn with soldering iron, and the surface tension is smoothed over the pin and the welding disc. Remove the flux from the board with alcohol after welding.
2. Welding method
A. PCB welding engineers remind everybody that before welding in the plate coated with flux, with iron processing again, in order to avoid bad solder tin or by oxidation, cause bad welding, chip is generally do not need to deal with.
B. Use tweezers to place the PQFP chip onto the PCB board carefully and be careful not to damage the pins. Align it with the welding disc to ensure that the chip is placed in the correct direction. The solder iron temperature to 300 degrees Celsius, the welding head pointed with a small amount of solder, use tools and hold down on the location of the chip, the two diagonal location pins and add a small amount of flux, still press the chips down, two diagonal position welding pin, make the chip is fixed and can't move. Re-check the position of the chip after welding. Adjust or remove and reposition the chip on the PCB board if necessary.
C.To start welding all pins, add solder to the tip of the soldering iron and apply all the pins to the flux to keep the pins moist. Contact the chip at the end of each pin with a soldering iron tip until you see the solder flow into the pin. In welding, the soldering iron tip should be kept in parallel with the welding pin to prevent lap joints from excessive soldering.
D.After welding all the pins, soak all pins with the flux to clean the solder. Remove excess solder to eliminate any short-circuit and lap joints where necessary. Finally, check with tweezers to see if there is false welding. After the inspection is completed, remove the flux from the circuit board, and wipe the hard brush with alcohol along the direction of the pin, until the flux disappears.
E.Circuit board welding engineers remind you that SMT some resistance capacity components is easier to weld, we can put tin on one of solder joint, and then put one end of the component, clamp the component with tweezers, after welding on one end, check if you're putting it right .If you have put it right, you can weld it to the other side. It takes a lot of practice to really master welding techniques.
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