Welding method of electric soldering iron on circuit board

1 in line pin type component welding method:


1.1 soldering iron head and two welding parts contact way.


(1) contact mode: the soldering iron head should be exposed to the connected 2 welded parts (such as welding pins and pads), and the soldering iron should be inclined to 30-45 degrees. When the two welding heating area of different components, should adjust the iron angle of the iron welding area with large welded components tilt angle decreases, the welding area of large welded parts contact area with the increase of iron, strengthen heat transfer ability. Such as LCD pull welding when the tilt angle of about 30 degrees, welding microphone, motor, horn and other tilt angle can be around 40 degrees. The two welded parts can reach the same temperature at the same time, and are regarded as the ideal state of heating.


(2): contact pressure and contact tip of welded parts should apply pressure, heat conduction intensity and pressure is proportional to size, but to be on the welding surface without causing damage to the principle of.


Method for supplying 1.2 solder wire


The supply of solder wire should master 3 essentials, both supply time, position and quantity.

(1) the time of supply: in principle, it is the temperature of the weldment to reach the melting temperature of the solder.

(2) supply position: it should be between the soldering iron and the weldment and close to the pad.

(3) the number of supply: should be seen the size of the weldment and the pad, solder cover after soldering tin solder higher than the diameter of the disc 1/3, the solder joints should be conical.


1.3 welding time and temperature setting


(1) the temperature is determined by the actual use, with a little tin welding 1-4 seconds is most appropriate, the maximum not more than 8 seconds, usually observe the iron head, when the blue when the temperature is too high.

(2) the line of electronic materials, the actual temperature of the soldering iron head set (350~370); surface mount materials (SMT), the actual temperature of the soldering iron head set (330~350 degrees), usually with 100 degrees of melting point solder.

(3) special materials, the need to set the temperature of soldering iron. LCD connector, such as the use of silver tin wire, the temperature is generally between 290 degrees to 310 degrees.

(4) the welding of large component feet, the temperature should not exceed 380 degrees, but can increase the power of iron.


1.4 welding precautions


(1) before welding should observe each solder joint (copper skin) is bright and clean, oxidation, etc., if there is debris to clean with a brush in the welding, if there is an increase in the amount of oxidation of the flux, in order to increase the welding strength.

(2) in the welding of goods, be sure to spot welding points, in order to avoid the short circuit caused by poor welding.

(3) if the component to be welded is a heat resistant package such as a molded case, it can be coated on the component body after being coated with anhydrous alcohol to prevent thermal damage.

(4) to carefully check the components after welding welding, solder joints around whether there is residual tin, tin, tin slag.


2 SMD component welding method:


2.1 in the welding before the first on the pad coated with flux, with iron handle again, so as to avoid the tin plate tin bad or oxidation, cause bad welding, the chip is generally no need to deal with.


2.2 carefully place the QFP chip on the PCB board with a pair of tweezers. Be careful not to damage the pin. Align it with the pad to ensure that the chip is placed in the right direction. The iron temperature to more than and 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 solder 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. Check the position of the chip after the end of the weld. If necessary, adjust or remove and re align the position on the PCB board.


2.3 start welding all the pins, should be in the iron tip with solder, all the pins coated with solder so that the pin to keep wet. Contact the end of each pin of the chip with a soldering iron tip until the solder enters the pin. In the welding to keep the tip of the iron and the welding pin in parallel, to prevent overlap due to excessive solder.


2.4 after soldering all the pins, wet all the pins with the flux to clean the solder. Remove excess solder from where needed, to eliminate any possible short circuit and overlap. Finally, with tweezers check weld inspection is completed, remove flux from the circuit board, the hard brush dipped in alcohol along the direction of pin carefully wipe, until the flux disappeared.


2.5 chip 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 it's straight; if it is placed, and then welded on the other end. If the pin is very thin in the second step can be added to the first chip pin tin, and then clamp the core with tweezers, at the side of the table light knock, pier in addition to the excess solder, the third step of the electric iron on the tin, soldering with iron. When we finish the welding work of a circuit board, we need to check the quality of the solder joints on the circuit board. Meet the following standards of solder joints we think is qualified solder joints:


(1) solder joint into inner arc (cone).

(2) the solder joints should be complete, smooth, no pinhole, no rosin.

(3) if there is a lead pin, the exposed pin length is between 1~1.2mm.

(4) the shape of the part of the foot can be seen as good fluidity.

(5) solder will surround the entire tin position and the parts.


 

(Source: Internal data)

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