PCB double back welding process

- Aug 18, 2018-

Circuit board assembly technology, now popular in the industry is Reflow, this technology can be divided into single panel back welding and double panel back welding.Single-face soldering is used less because double-face soldering saves circuit board space.

Double-sided soldering needs to be done twice, because of the limitation in the process, there will be some problems. For example, when the plate walks to the second soldering furnace, the parts on the first side will fall due to gravity, especially when the plate flows to the high temperature of the welding zone of the furnace.So, what should you mean when doing double-sided back welding manufacturing:

                          

Which SMD parts should be placed on the first side of the back welder?

First of all, it is suggested that the smaller parts should be placed in the first side back welding furnace, because the PCB deformation is relatively small when the first side is back welding furnace, and the printing precision of solder paste is relatively high, so the smaller parts should be put together.

Second, smaller parts do not risk falling over the second solder.Since the first part will be placed directly on the bottom of the circuit board when hitting the second side, it will not fall off the board due to the heavy weight when the board enters the backweld area at high temperature.

Parts again, the first side board must have two welding furnace back, so its heat resistance must can tolerate two back to welding temperature, average resistance capacitance is usually requires at least three times to welding heat, this is in order to comply with some boards may be because of the maintenance and the need to go once back in welding furnace's requirements.

Which SMD parts should be placed on the second side back solder?

1. Large or heavy components should be placed on the second side of the furnace to avoid falling back into the welding furnace.LGA and BGA parts should be placed as far as possible on the second side of the furnace so as to avoid unnecessary risk of tin remelting during the second pass and reduce the chance of air/false soldering.If there is a small BGA part with thin legs, it can also be placed on the first side of the back welding furnace, as long as it can effectively avoid PCB deformation.

2. Parts that cannot withstand too many times of high temperature should be placed on the second side of over-soldering furnace to avoid damage caused by too many times of high temperature.The part of PIH/PIP should also be placed on the second side of the furnace. Unless the length of its solder feet does not exceed the thickness of the plate, the feet extending from the PCB surface will interfere with the second side of the plate, which will make the second side of the solder paste printing plate unable to be flat on the PCB, thus causing the paste printing abnormality.

3. Soldering operation may occur inside some components, such as the wire connector with LED lamp. It should be noted that whether the temperature of this part can pass twice back to the welding furnace, or if not, the part must be placed on the second side of the stripper.

Just parts are put in the second plane hit a patch welding furnace back, it means the circuit board has passed a back to weld the baptism of the high temperature furnace, how much this time of the circuit board has some warping and deformation occur, that is the position of the amount of solder paste printing and printing will become more difficult to control, so also is likely to lead to problems such as empty or short circuit welding, so on the surface of furnace parts, suggested that try not to put a foot (fine pitch) between 0201 and fine parts, BGA should also try to choose a larger the diameter of the solder balls.

At present, the welding process of circuit board can be roughly divided into complete board welding and local welding, which can be roughly divided into Reflow Soldering and Wave Soldering, while the local welding of circuit board includes Carrier Wave Soldering, SelecTIve Soldering and non-contact Laser Soldering.