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Method of Enabling Ultra Thin WLCSP Packages

IP.com Disclosure Number: IPCOM000232248D
Publication Date: 2013-Oct-28
Document File: 8 page(s) / 2M

Publishing Venue

The IP.com Prior Art Database

Abstract

Conventional Wafer Level Chip Scale Packaging (WLCSP) requires a build-up process with a re-distribution layer to place solder ball interconnects within the die/package area. The build up process is relatively expensive compared to the standard wire bond assembly process. In addition, a different equipment set is required to assemble a WLCSP. In this paper, a low cost method of assembling a WLCSP is presented that can use conventional assembly process equipment.

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Document Title 

Method of Enabling Ultra Thin WLCSP Packages

Abstract 

Conventional Wafer Level Chip Scale Packaging (WLCSP) requires a build-up process with a re-distribution layer to place solder ball interconnects within the die/package area.  The build up process is relatively expensive compared to the standard wire bond assembly process.  In addition, a different equipment set is required to assemble a WLCSP.  In this paper, a low cost method of assembling a WLCSP is presented that can use conventional assembly process equipment.

Packaging Manufacturing Method 1:

A thin flex substrate is used as a distribution layer.  The flex substrate has a 2-step height design. The flex substrate may have either solder ball pads, or Au pads (similar to Land Grid Array (LGA)).  This process have to be done on relatively larger die sizes (>=7x7mm) whereby the dies are sawn and then placed onto a rectangular die carrier on top of high temperature adhesive tape.  The 2-step flex substrate is then attached onto the center of the die.  A fan-in wire bond process is performed to connect the bond pads to the lead fingers on the flex substrate using ultra-low loop bonding.  The overall package is completed through over-molding over the dies and substrate, with the upper layer of the flex substrate exposed, followed by ball attach process, if solder ball pads are used.  Finally, the packages are sawn into individual units, and then followed by pick and place and FOI.

FIGURE 1: Process Assembly flow of Method 1

                            FIGURE 2: Placement of Sawn Die onto the Die Carrier

FIGURE 3: Place flex substrate

FIGURE 4: Over-mold

FIGURE 5:  Package Singulation

Packaging Manufacturing Method 2:

Ultra thin WLCSP process is performed starting from wafer form where back grinding of the wafer is done to reduce the thickness.  An interposer is fabricated in strip forms (with maximize #unit/strip that the process can take), pre-singulated before the interposer attach process to the die top, followed by attaching the interposer on top of the die surface (interposer...