what should be done when manufacturing double-sided reflow soldering?
Now board assembly technology is popular in the industry full-flow reflow soldering (Reflow). This technology can be divided into single-panel reflow and double-plane reflow soldering. One-sided soldering is used less frequently because double-sides reflow soldering can save board space.
Two-sided reflow requires two reflows. Due to process limitations, problems may arise. For example, when the board reaches the second reflow furnace, parts above the first surface will fall due to gravity, especially the board flows to the reflow zone of the furnace at high temperatures. So, what should be done when manufacturing double-sided reflow soldering?
Which SMD parts should be placed on the first side of the reflow oven?
First of all, the relatively small parts are recommended to be placed on the first side of the reflow furnace, because the first side of the reflow furnace when the PCB deformation will be relatively small, the solder paste printing accuracy will be relatively high, so more than one placed Smaller parts.
Second, the smaller parts do not have the risk of dropping when they pass through the oven for the second time. Because the part of the first side will be placed on the bottom surface of the circuit board directly downwards when playing the second side. When the board enters the high temperature of the reflow area, it will not drop from the board due to the excessive weight.
Again, the parts on the first panel must go through the reflow oven twice, so its temperature must be able to withstand the temperature of the two reflows. The common resistors and capacitors are usually required to have at least three reflow temperatures. This is to comply with Some boards may need to go through the reflow oven once again due to maintenance.
Which SMD parts should be placed on the second side of the reflow oven?
1, Large components or heavier components should be placed on the second side of the furnace, in order to avoid parts falling back to the furnace furnace. The LGA and BGA parts should be placed on the second side of the furnace as much as possible to avoid the risk of unnecessary re-melting of the tin during the second pass to reduce the chance of air/pass welding. If there are finer and smaller BGA parts, it can also be placed on the first side of the reflow oven, as long as it can effectively prevent the PCB deformation.
2, Parts can not withstand too many times high temperature should be placed on the second side of the reflow oven, this is to avoid parts too many times high temperature and damage. Parts of PIH/PIP must also be placed on the second side of the furnace, unless the length of the welding leg does not exceed the thickness of the plate, otherwise its feet protruding from the surface of the PCB will interfere with the steel plate on the second side, which will make the second side Paste-printed steel plates cannot be flatly attached to the PCB, resulting in abnormal solder paste printing.
3, Some components will use soldering inside the case, for example, there is a LED cable connector, must pay attention to the temperature of this part can be twice the reflow furnace, if you can not be placed on the second side to play Pieces.