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The IP.com Prior Art Database
Disclosed is a method for a soldermask-defined pad (SMDP). Benefits include improved reliability, and improved design flexibility.
United States
English (United States)
Method for a soldermask-defined pad
Disclosed is a method for a soldermask-defined pad (SMDP). Benefits include improved reliability, and improved design flexibility.
Background
� � � � � Testing of conventional 1-mm packages with different PCB design configurations has shown that SMDPs are a critical-to-function parameter for passing Reliability requirements.
� � � � � Failures are thermal expansion related and improved shear strength improves reliability. When applying shear or thermal expansion force, the forces distributed across three planes improve shear strength over the shear strength of one or two planes. Data has proven that the reliability of mask-defined pads (MDPs) is much better than that of SMDP. The reason for this result is tied to directional shear strength. The solderball for MDPs provides increased X/Y shear strength due to Z-axis coverage of the solder to the metal foot.
� � � � � Package size and rout out density within the PCB are limited by the requirement to use larger SMDP designs.
� � � � � The smallest SMDP without failure is a 16.9-mils target. With that size SMDPs, 2-track routing is only achievable with 4/4 trace/space technologies that have a cost premium. To use 14.4mil SMDPs, the reliability issue must be resolved.
� � � � � The conventional method has the following characteristics (see Figure 1):
• � � � � No break in the Cu/Sn/Pb intermetallic along the X/Y plane
• � � � � Reduced copper-to-tin/lead bondable surface area
• � � � � Shear or thermal expansion force that is all applied along the X/Y plane
General description
� � � � � The disclosed method is a PCB design with an etch feature (such as clearance pad, X-etch, or other) within the SMDP metal area that impr...
