![]() I will check all of this again, very annoying situation. Also, I have the same resistor in several locations on the board, if it was a placement pressure problem I would see the same on all. I suspected the placement pressure, but I don't want to push too much as resistors break. The solder reflow profile is one of the key variables in the manufacturing process that significantly impacts product yield. Funny, while this is happening with 0805 resistors, I have on the same board 2 tantalum caps size D placed quite close to each other in parallel and one of the pads is connected to a large shield surface without thermal relief, never had any problem with them. The thermal mass of the pads, at least where this phenomena happens is equal. The machine placements are very precise and each board is inspected before reflow. Learn about reflow profiles when working. But you mentioned very logical causes and there is some thinking to do, in addition to the possible bad ENIG plating. Solder paste is approximately 50 flux by volume and not all of this flux can be evacuated from the solder joint during reflow. Ray Prasad lends his experience to his SMT articles, with information on ball grid arrays, including lead-free BGA. In most places it is associated to poor wetting, while tombstone is commonly associated with uneven pads or one pad connected to a large surface without thermal relief. Thanks wraper, I read a lot about possible causes to this problem, can say for sure that although it looks the same there is a difference between tombstoning and what I am describing. ![]()
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