SOLDER JOINTS FOR SURFACE MOUNT CHIPS

摘要

There is disclosed herein a surface mount printed circuit board having a substrate (10), at least one surface mount device (14), at least two mounting pads (12) per device (14), solder joints (24) connecting the terminations (22) of the device (14) to their respective mounting pads (12), at least one rectangular lifter pad (30) on the substrate (10) amid the mounting pads (12), and a solder mass (32) on each lifter pad (30) in contact with the bottom surface (18) of the device (14). The solder joint (24) has preferably convex outer fillets (28), the device (14) is maintained at a predetermined height (ho) above the mounting pads (12), the inner fillet angle ( alpha ) is maintained above a predetermined minimum angle to increase solder joint crack initiation time, and the overall solder joint crack propagation length is increased (li and lo). An alternative embodiment also includes plugged vias (34) under the lifter pads (30) and/or mounting pads (12), with gas pockets (40) trapped between the solder masses (32)/solder joints (24) and the plugged vias (34). This trapped gas pocket (40) provides additional buoyant force upon the SMD (14) during reflow.