EFFECTS OF PAD SIZE VARIATIONS, SOLDER MASK REGISTRATION, AND SUBSTRATE WARPAGE ON DIRECT CHIP ATTACH ASSEMBLY YIELDS
Author: Krishna Kalyan Company: State University of New York Date Published: 4/28/1997
Surface Mount International
Abstract: Direct Chip Attach (DCA) technology is being studied and increasingly used in the electronics packaging arena to achieve product miniaturization with concurrent product size reduction. The constraints imposed by the pitches and the high Input/Output (1/0) count pose significant challenges to board manufacturers. The pitches involved in DCA technology may be as low or lower than 10 roils, while the 1/0 counts on the DCA component may be as high as 1000. Further, the orientation of pads could be depopulated, area array, or asymmetric. These factors often result in variations in the pad and solder mask dimensions, which may consequently exert a significant influence on DCA assembly yields. The pad dimensions in Printed Circuit Boards (PCBS) that are used in DCA assembly are typically about 5 roils. These fine pitches, dimensions, and the high 1/0 counts cause the DCA component assembly process to be extremely sensitive to different material and process parameters. Although the individual process and material related variations may seem innocuous by themselves, the combined effects of these variations may limit assembly yields. The factors that affect DCA assembly yield can be categorized as board related, component related, and process related. This study focussed on some of the board related issues that would affect DCA assembly yields.