Investigation Into How the Floor Plan Layout of a Manufactured PCB Influences Flip-Chip Susceptibility to Vibration.

This article investigates how floor plan layout of a printed circuit board (PCB) influences the reliability of the component’s solder joint connections when operated in a vibrating environment. A random vibration profile as seen in an automotive environment was used in full lifetime tests. An industry-standard FR4 PCB with electroless nickel immersion gold (ENIG) surface finish was manufactured with double-sided component placement including 14 flip chips, eight on the top side and six on the bottom side. Ultrasound scans were used as a nondestructive test to assess the integrity of solder joints from manufacture to failure. This enabled monitoring of the important interface between solder joints and flip chip where failure mostly occurs. The initial failure pattern was found by experiment where 86 cycles of random vibration caused all flip chips to mechanically fail. Failure followed a Weibull probability with a value of $\beta = 1.297$ , indicating that failure rates increase with time. The results show that the reliability of a flip chip varies with its position on a PCB with some marked differences to component lifetimes. The results also show that for two-sided flip-chip placements on a PCB, back-to-back, overlapped, and single-sided orientations have subtle effects on flip-chip lifetimes. Similarly, reliability varied with solder joint positions since joints on the sides of a flip chip nearest the PCB edges were less reliable than those on sides on a flip chip furthest away. Finally, design guidelines are offered to effect the most reliable flip-chip placement on a two-sided PCB when operated in a vibrating environment. [ABSTRACT FROM AUTHOR]