In this tutorial we are going to learn about what is Solder Mask & Non Solder Mask?
Surface land pads are means where the areas on the PCB to which the BGA solder balls adhere. The size of these pads affects the space available for vias & escape routing. Generally, surface land pads are available in the Following two basic designs:
Solder mask defined (SMD): The main differences between the 2 surface land pad types are the size of the trace & space, the type of vias you can use, & as usual the shape of the solder balls after solder reflow.
Solder Mask Defined (SMD) Pad: The SMD pad process uses the solder mask to define the usable pad. The copper for the pad area is usually larger than the desired solder able area. The solder mask provides a smaller opening dia which limits the usable area to the desired size. The advantages to this method are:
• The solder mask is a photographically controlled instead of being at the mercy of the etch process.
• The solder mask enhances copper adhesion by lying over the top of the pad surface.
Non-Solder Mask (Copper) Defined Pad: The non-solder mask is defined pad has a solder mask opening larger than the copper area. Generally, the pad periphery is left under the control of the etching process. As expected, this process is generally not as accurate as the solder mask photo image control described above. While pad size varies more than with the SMD method, the pads can be made smaller for the same ball area. This allows additional line routing space between pads. Land Pattern registration is also more accurate with this method. This may be an advantage to vision systems since registration on copper reference points will give the exact location of the site. Relying on the solder mask can cause miscues because of variances in the site location relative to vision reference points.