Browse Prior Art Database

Method to attach a flip-chip die to a package without preapplying solder on the package bump pad using a eutectic column bump shape

IP.com Disclosure Number: IPCOM000011738D
Publication Date: 2003-Mar-12
Document File: 4 page(s) / 104K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method to attach a flip-chip die to a package without preapplying solder on the package bump pad using a eutectic column bump shape. Benefits include improved functionality, improved performance, improved design flexibility, improved ease of manufacturing, and improved yield.

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Method to attach a flip-chip die to a package without preapplying solder on the package bump pad using a eutectic column bump shape

Disclosed is a method to attach a flip-chip die to a package without preapplying solder on the package bump pad using a eutectic column bump shape. Benefits include improved functionality, improved performance, improved design flexibility, improved ease of manufacturing, and improved yield.

Background

              An overhang nonstick issue occurs with the conventional flip-chip attachment process if a substrate is designed with a pad without solder and with a small solder resist opening (SRO).

              In the conventional flip-chip attachment process, eutectic bumps are reflowed to a round shape at die preparation before attaching the chip. With a substrate design with a pad without solder and with a small SRO, the round die bump can be too big. The small SRO can overhang the bumps and prevent the direct contact between the bump and the substrate pad surface (see Figure 1).

              During high temperature reflow the round die bump melts only partially and is not able to flow into the solder resist defined pad opening to make contact with the pad. The result is the overhang non-stick phenomenon (see Figure 2 with the bump and solder resist opening at the left-hand side). No known solution exists for this problem.

              The quality of the joint between the rounded die bump and the substrate pad depends on the melting of the die bump during chip-attach reflow. If the reflow timing is right for the fluxing reaction and solder melting, a good joint can be formed (see Figure 2, bump at the right-hand side). However, the joint between the rounded die bump and the substrate pad may not form because the fluxing reaction (solder deoxidation by the flux) does not occur at the correct time (see Figure 1, bump at the left-hand side). The die bump may melt after the flux is no longer effective to remove the oxidation layer of the solder surface, causing a non-stick.

              Conventionally, flip-chip attachment is only possible if a substrate has solder on the pad or if a substrate without solder on the pad has a large enough SRO. For an input/output (I/O) product with <100 bumps/unit, a chip joint between a bumped flip-chip to a substrate without solder on the pad is feasible, but an SRO >120 µm is required. For an I/O product with >100 bumps/unit, a substrate with solder on the pad is required in addition to the SRO >120 µm to form the bump joint.

General description

              The disclosed method is a eutectic column bump shape (with a small contact surface tip) for flip-chip attachment to a substrate with a small SRO and without solder on substrate pad. With a small tip column bump, solder bumps can be inserted into the small SRO. The eutectic bump melts and makes contact with the substrate pad during the chip attach reflow process.

              The key elements of the method include:

•             Plated solid eutectic...