# US 7,743,966 B2 · Soldering flux and method for bonding semiconductor element

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- Number: US 7,743,966 B2
- Document ID: US7743966B2
- Status: Granted
- Kind: B2
- Application number: 11/475,001
- Filed: 2006-06-27
- Published: 2007-09-27
- Granted: 2010-06-29
- Earliest claimed: 2006-03-27
- Assignees: Fujitsu Limited
- Inventors: Toshiya Akamatsu; Seiki Sakuyama
- Web page: https://patentgrep.com/patent/US7743966B2

## CPC

- B23K 3/0623: {for shaped solder piece feeding, e.g. preforms, bumps, balls, pellets, droplets}
- B23K 1/203: {Fluxing, i.e. applying flux onto surfaces}
- B23K 2101/40: Semiconductor devices
- H10W 74/15: on active surfaces of flip-chip devices, e.g. underfills
- H10W 90/724: {between a chip and a stacked insulating package substrate, interposer or RDL}
- H10W 90/734: {between a chip and a stacked insulating package substrate, interposer or RDL}
- B23K: SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- H10W: GENERIC PACKAGES, INTERCONNECTIONS, CONNECTORS OR OTHER CONSTRUCTIONAL DETAILS OF DEVICES COVERED BY CLASS H10

## Abstract

The method for bonding a semiconductor element comprises the step of applying to solder bumps 10 of a semiconductor chip 12 a soldering flux 16 which contains a thermosetting resin, a polyhydric alcohol and an organic acid and in which the thermosetting resin remains uncured after reflow-bonding, the step of reflow-bonding the solder bumps 10 to the electrodes 18 of the circuit board 20 with the soldering flux 16 while melting the solder bumps 10, and the step of filling an underfill material 22 between the semiconductor chip 12 and the circuit board 20 with the soldering flux 16 being left, the underfill material 22 containing a thermosetting resin of the same group as the thermosetting resin contained in the soldering flux 16 and at least one of a curing agent and a cure catalyst for curing the thermosetting resins.

## Claims

### Claim 1

A method for bonding a semiconductor element, which includes reflow-bonding a solder bump formed on a first substrate to an electrode formed on a second substrate, comprising:
applying a soldering flux to be used in reflow-bonding the solder bump formed on the first substrate to the electrode formed on the second substrate, comprising: a first thermosetting resin, a polyhydric alcohol and an organic acid, the soldering flux not including a curing agent or a cure catalyst;
reflow-bonding the solder bump to the electrode with the soldering flux which is not cured while melting the solder bumps without curing the first thermosetting resin thereby keeping the soldering flux uncured;
filling an underfill material between the first substrate and the second substrate with the soldering flux which is not cured being left, the underfill material including a second thermosetting resin of the same group as the first thermosetting resin and at least one of a curing agent and a cure catalyst for curing the first and the second thermosetting resins; and
after filling an underfill material to compatibly mix the first and the second thermosetting resins, heating to cure the first and the second thermosetting resins compatibly mixed with each other.

### Claim 2 (depends on 1)

A method for bonding a semiconductor element according to claim 1, wherein
the second thermosetting resin is bisphenol F cyanate ester, bisphenol A cyanate ester, or phenol novolak resin cyanate ester.

### Claim 3 (depends on 1)

A method for bonding a semiconductor element according to claim 1, wherein
the underfill material contains the cure catalyst when the first and the second thermosetting resins are cyanate ester-based resins.

### Claim 4 (depends on 1)

A method for bonding a semiconductor element according to claim 1, wherein
the underfill material contains the curing agent when the first and the second thermosetting resins are epoxy-based resins.