This allows connection from the chip core to the pad. The bonding pad is made from all metal layers stacked on top of each other and connected through the vias. One side of a gold wire will connect to the bonding pad while the other side will connect to the package. Via-in-pads are used for BGA components with pitches of 0.5 mm or lesser.ĭOWNLOAD OUR HIGH-SPEED PCB DESIGN GUIDE:Ī bonding pad serves the purpose of connecting the circuit on a die to the pin on a packaged chip. Via-in-pad is used to minimize the form factor of a PCB by reducing the space taken up by trace routing. Conventional vias have signal carrying traces routed away from the pad and to the via. In HDI designs, where space is a constraint it becomes necessary to place vias on pads. The different parts of a through-hole pad are typically called a pad stack, which consists of:Ĭan you put a via on a pad? – Yes, as a via-in-pad This is done to prevent shorts between copper layers and parts that are to be placed. Conventionally, unplated holes will have an area around the hole that is clear of any copper (similar to board edge clearance). This pad is mostly used for single-sided boards or these holes are used for mounting the PCB in an enclosure and screws are mounted through these holes. NPTH refers to a pad without plating in the hole.
The plating provides for electrical connection between the different layers of the board. The hole plating is done using the process of electrolysis. The hole wall will be plated with copper and sometimes with solder or another protective plating. Pads used to mount through-hole components are called through-hole pads and are of two types: The plated through-hole (PTH) However, NSMD pad delamination can be prevented when standard manufacturing and handling practices are followed. One disadvantage of NSMD pads is their high susceptibility to delamination due to thermal and mechanical stresses. 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. 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 Pad number (number of pads present for the component).This can be rectangle, round, square, or oblong. Pads used to mount surface mount components are called surface mount pads. Pad design for through-hole pads Surface mount pads