Browse Prior Art Database

ENHANCE SELF ALIGNMENT DIRECT CHIP ATTACH

IP.com Disclosure Number: IPCOM000009819D
Original Publication Date: 2000-May-01
Included in the Prior Art Database: 2002-Sep-20
Document File: 3 page(s) / 189K

Publishing Venue

Motorola

Related People

CL Wong: AUTHOR

Abstract

The present DCA process using the Control Collapse Chip Connection (C4) technology requires pre-deposited solder on the DCA site on the Printed Circuit Board (PCB). The solder deposit on the DCA site on the PCB is typically flattened. (Figure 1). In DCA process, the DCA site on the PCB is first fluxed, then the flip chip die is placed on the PCB with the corresponding flip chip bumps sitting on the pre-deposited solder bumps and lastly the assembly is reflowed.

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MOTOROLA

Technical Developments

ENHANCE SELF ALIGNMENT DIRECT CHIP ATTACH

by CL Wong

BACKGROUND

The present DCA process using the Control Collapse Chip Connection (C4) technology requires pre-deposited solder on the DCA site on the Printed Circuit Board (PCB). The solder deposit on the DCA site on the PCB is typically flattened. (Figure 1). In DCA process, the DCA site on the PCB is first fluxed, then the flip chip die is placed on the PCB with the corresponding flip chip bumps sitting on the pre-deposited solder bumps and lastly the assembly is reflowed.

During reflow, the pre.deposited solder will melt and wet to the solder bump flip chip, hence forming a mechanical and electrical connection between the PCB and the die.

PROBLEM

The issue that is seen here is that because the pitch of DCA is typically only at 10 mils, the alignment of the DCA chip on the pre-deposited solder bumps on the PCB is very critical in order to fom1 a good solder interconnection.

In addition, the presence of liquid flux increases the tendency of the flip chip die to move during the reflow process.

Motorola. Inc. 2000

(Figure 3) Movement of the die will cause problems such as unsolder on the flip chip solder bumps.

SOLUTION TO THE PROBLEM

The new invention is on the structure of the predeposited solder bumps on the PCB. The new design of the pre.deposited solder has cavity of 10 mils in diameter. (Figure 4 and 5).

With the cavity on the pre-deposited solder bumps, the flip chip die when placed on the PCB will have the flip chip solder bumps sitti...