![]() This approach leaves more room between adjacent pads enabling easier trace routing and is used for high density and fine pitch BGA chips. NSMD pads can be smaller than the diameter of the solder ball, and this reduction in pad size is 20% of the ball diameter. Here the copper pad size is defined by the copper pad diameter instead of the mask layer. The mask is instead created such that a gap is generated between the pad edge and the solder mask. ![]() NSMD pads vary from SMD pads in that the solder mask is defined to not contact the copper pad. SMD and NSMD pads Non-solder mask defined BGA pads (NSMD) To generate the SMD overlay, a reduction of 20% is traditionally used. ![]() The copper layer of an SMD BGA pad conventionally has a diameter equal to the pad on the BGA. The second advantage is that the opening in the mask will create a channel for every ball on the BGA to align with while the part moves through the soldering process. This can lead to two advantages – firstly, the overlapping mask helps prevent the pads from lifting off the board because of mechanical or thermal stress. The image shows how the solder mask has been specified to cover a part of the copper pad underneath. This is done to shrink the copper pad size that the part will be soldered to. These pads have the solder mask aperture such that the mask opening is smaller than the diameter of the pad they cover. SMD pads are defined by the solder mask apertures applied to the BGA pads. There are basically two types of BGA pads – the solder mask-defined pad (SMD) and the non-solder mask-defined pad (NSMD). Proper pad design is critical to ensure the manufacturability of BGA components. Special features of BGA pad SMD pad vs NSMD pad
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