COMPONENT PACKAGES

WLCSP Component Package

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Date Published:	March 24, 2015
Last Modified:	March 24, 2015

Overview

Name	Wafer-level Chip-scale Package (WLCSP)
Synonyms	LCSPW (W has changed position)
Variants	n/a
Similar To	BGA
Mounting	SMD
Pin Count	4-144
Pitch	0.3-0.5mm
Solderability	Cannot be soldered with a soldering iron. Requires reflow oven or infrared heater.
Thermal Resistance	n/a
Land Area	n/a
Height	n/a
3D Models	n/a
Common Uses	Op-amps

Comments

The WLCSP package can either be rectangular or square in shape.

The pin numbering follows the standard BGA convention, the columns are labelled with letters (A, B, C, …) and the rows with numbers (1, 2, 3, …). Thus pins are referred to as A1, C3, D11, e.t.c.

The rows of bumps maybe aligned in a grid or offset, again like BGA.

As of March 2015, WLCSP offers the smallest possible footprint of any component package for a particular die ((https://www.fairchildsemi.com/application-notes/AN/AN-5075.pdf)).

Photosensitivity

Unusually, the WLCSP package is sensitive to high-intensity, long wavelength light. This was due to the photoelectric effect, where the light hitting the top and sides of the semiconductor-based package causes current to flow in the die and can disrupt proper operation.

WLCSP packages can come with a backside laminate (BSL) which blocks light from disrupting the IC. Fairchild Semiconductor explain that having a BSL is not significant for board-level reliability.

Paragraph on backside laminate (BSL) for WLCSP component packages. Image from https://www.fairchildsemi.com/application-notes/AN/AN-5075.pdf.

RaspberryPi 2 Bug

The photosensitivity of the WLCSP package manifested itself as a bug on the RaspberryPi 2. The regulator that provided power to the RaspberryPi 2 core was in a WLCSP package, and when exposed to a high-intensity, long wavelength light (like a xenon camera flash), the RaspberryPi 2 would reset.

The current caused by “normal” camera flashes do not seem to be able to permanently damage the chip.