PCF8883USSLASH7EASLASH1 datasheet(28/35 Pages) NXP

28 / 35 page

PCF8883

All information provided in this document is subject to legal disclaimers.

Product data sheet

Rev. 4.1 — 14 September 2016

28 of 35

NXP Semiconductors

PCF8883

Capacitive touch/proximity switch with auto-calibration

• The bump height on the chip

The higher the stand off, the better the stresses are released due to TEC (Thermal

Expansion Coefficient) differences between substrate and chip.

20.3.2 Quality of solder joint

A flip-chip joint is considered to be a good joint when the entire solder land has been

wetted by the solder from the bump. The surface of the joint should be smooth and the

shape symmetrical. The soldered joints on a chip should be uniform. Voids in the bumps

after reflow can occur during the reflow process in bumps with high ratio of bump diameter

to bump height, i.e. low bumps with large diameter. No failures have been found to be

related to these voids. Solder joint inspection after reflow can be done with X-ray to

monitor defects such as bridging, open circuits and voids.

20.3.3 Rework

In general, rework is not recommended. By rework we mean the process of removing the

chip from the substrate and replacing it with a new chip. If a chip is removed from the

substrate, most solder balls of the chip will be damaged. In that case it is recommended

not to re-use the chip again.

Device removal can be done when the substrate is heated until it is certain that all solder

joints are molten. The chip can then be carefully removed from the substrate without

damaging the tracks and solder lands on the substrate. Removing the device must be

done using plastic tweezers, because metal tweezers can damage the silicon. The

surface of the substrate should be carefully cleaned and all solder and flux residues

and/or underfill removed. When a new chip is placed on the substrate, use the flux

process instead of solder on the solder lands. Apply flux on the bumps at the chip side as

well as on the solder pads on the substrate. Place and align the new chip while viewing

with a microscope. To reflow the solder, use the solder profile shown in application note

AN10365 “Surface mount reflow soldering description”.

20.3.4 Cleaning

Cleaning can be done after reflow soldering.

PCF8883US/7EA/1 Datenblatt(PDF) 28 Page - NXP Semiconductors