Joy Technology Co.,Limited

Hand soldering techniques | Welding methods | Patch components
More and more circuit boards use surface mount method, compared with the traditional package, it can reduce the area of the circuit board, easy to bulk processing, wiring density. Chip resistors and capacitors lead inductance greatly reduced, in the high-frequency circuit has great advantages. The inconvenience of surface mount components is not easy for manual soldering. To this end, this paper to the common PQFP package chip, for example, describes the surface mount components of the basic welding method.
First, the required tools and materials
Welding tools need to have 25W copper head small soldering iron, conditional and can be used to adjust the temperature and ESD protection of the welding station, pay attention to the soldering iron tip to the top, the width of the top can not be greater than 1mm. A pointed tweezers can be used to move and fix the chip as well as check the circuit. But also to prepare fine wire and flux, isopropyl alcohol and so on. The purpose of using flux is to increase the solderability of the solder, so that the soldering can be traction with a soldering iron, and rely on the role of surface tension smoothly wrapped in the pin and pad. Remove the flux from the plate with alcohol after welding.
Second, the welding method

1. Apply the flux to the pad before welding, and treat it with a soldering iron to prevent the solder pad from being bad or oxidized, causing poor welding. The chip is generally not required to be treated.

2. Carefully place the PQFP chip on the PCB with tweezers, taking care not to damage the pins. Make it aligned with the pad, to ensure that the chip placed in the correct direction. The temperature of the soldering iron transferred to more than 300 degrees Celsius, the tip of the tip with a small amount of solder, with the tool down to hold the alignment of the chip, the two diagonal position of the pin with a small amount of flux, Hold down the chip, welding the two diagonal position on the pin, so that the chip fixed and can not move. After rewriting the diagonal, check the chip position is aligned. If necessary, adjust or remove and re-align the PCB board.

3. When starting all the pins, solder the solder tip and apply solder to the pins so that the pins are kept moist. Touch the tip of each pin with the tip until you see the solder flow into the pin. In the welding to keep the tip and the welding pin parallel to prevent the occurrence of excessive overlap due to solder.

4. After soldering all the pins, wet all pins with solder to clean the solder. Absorb any excess solder in the place where you need to eliminate any short circuit and lap. Finally, with tweezers to check whether there is Weld, check the completion of the removal of flux from the circuit board, the bristle brush soaked in alcohol along the direction of the pin carefully wipe until the flux disappeared.

5. Patching resistance element is relatively easy to weld some, you can first point on a solder point on the tin, and then put a component of the end, with tweezers clamped components, welded on a head, and then see if it is put; Put on, and then welding another one. To really master the welding skills require a lot of practice.If the pin is very fine in the first two steps when you can first chip pin tin, and then clamp the chip with tweezers, at the table light knock, pier in addition to excess solder, step 3 Electric soldering iron do not have tin, with soldering iron direct welding. When we complete a circuit board welding work, it is necessary to check the quality of the solder joint on the circuit board, repair, repair welding. Meet the following standard solder joints we believe is qualified solder joints:
(1) the solder into the inner arc (conical).
(2) the overall solder joints to be successful, smooth, no burr, no rosin stains.
(3) If there are leads, pins, their exposed pin length to between 1-1.2MM.
(4) part of the foot shape visible tin good dispersion.
(5) The solder will surround the entire tin position and the foot of the part.   Do not meet the above criteria of the solder joint we believe that is not qualified solder joints, the need for secondary repair.
(1) Weld: seemingly welded actually did not weld, the main reason is the pad and pin dirty, lack of flux or heating time is not enough.
(2) short circuit: foot parts between the feet and feet by the excess solder connected  to the short circuit, including residual tin slag to foot and feet short circuit.
(3) Offset: As the device is not positioned before welding, or in the welding caused by  errors lead to the pin is not within the provisions of the pad area.
(4) less tin: less tin refers to the tin point is too thin, can not fully cover the copper parts, affecting the role of fixed connection.
(5) multi-tin: part of the foot is completely covered with tin, that is, the formation  of external arc, so that parts shape and pad can not be seen, can not determine        whether the parts and pads on the tin good.
(6) solder ball, tin slag: PCB board surface attached to the excess solder ball, tin slag, will lead to small pin short circuit.