Wafer Level Chip Scale Package (WLCSP) devices are used because they offer low cost, small footprint packages to be directly mounted into smartphones, tablet PC's and other mobile devices and meanwhile even in automotive applications. The manufactures of these mobile and automotive application devices are demanding lower defect parts per million (DPPM) from their suppliers of WLCSP devices.
Today, the backend process flow for mobile WLCSP devices is a single insertion test at wafer probe. With this flow, there is no test that is done after device singulation (wafer saw). The reason for this flow is that there has been no cost effective way to handle singulated WLCSP devices in a high volume manufacturing environment.
Xcerra's proposal is using InCarrier (device carrier) technology to solve this market requirement. InCarrier technology was designed to secure up to hundreds of singulated devices in an array similar in format to a device strip. By placing the singulated devices into an InCarrier, the InStrip device handler can then be used to provide Final Tri-temp Test of WLCSP devices.
This paper will explore some of the key attributes and technical challenges in testing singulated WLCSP devices. Topics to be explored include:
- Backend process flow and machinery required
- Device handling, alignment and retention of delicate WLCSP devices
- Device placement accuracy required for multi-site test of WLCSP and impact on yield
- Methodology to retain data for wafer map even though wafer sort test is not done
- Test cell efficiency gain enabled by InCarrier
InStrip / InCarrier WLCSP solution is in development now and is planned to be evaluated in a HVM before the Semicon Penang conference.