Tom
10-23-2002, 02:41 PM
IPC Advanced Study Guide Page Reference: Pages 33, Section 1.4
With the advent of ball grid arrays, the issue of tenting and mask clearances became a major concern for many designers. Initially a debate existed between the use of solder mask defined lands vs. non-solder mask defined lands.
The following illustration provides information as to the relationship between the copper land, the solder mask, and a via intended to make continuity to innerlayers.
The non-solder mask defined lands require a smaller diameter copper land and therefore have more metal-to-metal spacing for routing and vias. Copper dimensions can also be controlled better than solder mask dimensions giving a more uniform surface finish, especially for HASL boards. The absence of solder mask on the copper land allows the BGA solder ball to collapse and flow around the edges of the land, eliminating any areas of stress concentrations.
This makes the solder joint larger, potentially giving it longer fatigue life, but also lowers the standoff height.
With the advent of ball grid arrays, the issue of tenting and mask clearances became a major concern for many designers. Initially a debate existed between the use of solder mask defined lands vs. non-solder mask defined lands.
The following illustration provides information as to the relationship between the copper land, the solder mask, and a via intended to make continuity to innerlayers.
The non-solder mask defined lands require a smaller diameter copper land and therefore have more metal-to-metal spacing for routing and vias. Copper dimensions can also be controlled better than solder mask dimensions giving a more uniform surface finish, especially for HASL boards. The absence of solder mask on the copper land allows the BGA solder ball to collapse and flow around the edges of the land, eliminating any areas of stress concentrations.
This makes the solder joint larger, potentially giving it longer fatigue life, but also lowers the standoff height.