AN824

Vishay Siliconix

Document Number: 71990

06-Jan-03

www.vishay.com

1

PCB Design and Assembly Guidelines

For MICRO FOOTr Products

Johnson Zhao

INTRODUCTION

Vishay Siliconix’s MICRO FOOT product family is based on a

wafer-level chip-scale packaging (WL-CSP) technology that

implements a solder bump process to eliminate the need for an

outer package to encase the silicon die. MICRO FOOT

products include power MOSFETs, analog switches, and

power ICs.

For battery powered compact devices, this new packaging

technology reduces board space requirements, improves

thermal performance, and mitigates the parasitic effect typical

of leaded packaged products. For example, the 6−bump

MICRO FOOT Si8902EDB common drain power MOSFET,

which measures just 1.6 mm x 2.4 mm, achieves the same

performance as TSSOP−8 devices in a footprint that is 80%

smaller and with a 50% lower height profile (Figure 1). A

MICRO FOOT analog switch, the 6−bump DG3000DB, offers

low charge injection and 1.4 W on−resistance in a footprint

measuring just 1.08 mm x 1.58 mm (Figure 2).

Vishay Siliconix MICRO FOOT products can be handled with

the same process techniques used for high-volume assembly

of packaged surface-mount devices. With proper attention to

PCB and stencil design, the device will achieve reliable

performance without underfill. The advantage of the device’s

small footprint and short thermal path make it an ideal option

for space-constrained applications in portable devices such as

battery packs, PDAs, cellular phones, and notebook

computers.

This application note discusses the mechanical design and

reliability of MICRO FOOT, and then provides guidelines for

board layout, the assembly process, and the PCB rework

process.

FIGURE 1. 3D View of MICRO FOOT Products Si8902DB and

Si8900EDB

FIGURE 2. Outline of MICRO FOOT CSP & Analog

Switch DG3000DB

0.18 ~ 0.25

32

1

A

B

0.5

1.58

0.5

0.285

0.285

1.08