If the circuit board needs to be printed on both sides (side1, side2 or side A, side B) SMT, which side should be printed first? How is the first side to be played? What is the decision point? Editor: This problem is a bit more complicated. Generally speaking, at the beginning of the product design, it is necessary to decide which parts are placed on the first side and the second side according to the DFM (Design For Manufacturing) design specification. It’s just that sometimes things go against their wishes, and the SMT factory may not be able to make any DFM recommendations.
Think about it when the parts on the first side of the board are finished, when the parts on the second side are to be hit, the original parts on the first side will be turned over and put down, and then after the second side is finished, the parts will be passed again. In a high-temperature reflow furnace, if there are heavier parts on the bottom surface (first side) at this time, it will fall off easily due to gravity and the possibility of remelting the solder paste when the reflow furnace is passed through the second time. So generally the side with heavier parts will be placed on the second side to print.
Secondly, when there are BGA or LGA parts, because they are worried that the second pass will affect the drop and the solder reflow problem, it is recommended to put the parts on the second side and only pass the reflow furnace once. If there are other parts with fine pitch (fine pitch) parts, because they need more precise alignment, under normal circumstances, if you can print on the first side, it will be better than the second side, because the circuit board After a reflow oven, the board is easily bent and deformed due to the influence of temperature, which will cause the offset of the solder paste printing, and the amount of solder paste is not easy to control well. Of course, these are just principles, and there are often exceptions, because the double-sided SMT process has some inherent limitations, so it is just to choose a step that has the least impact on the process and the quality can be optimized.