Method for joining electronic parts finished with nickel and electronic parts finished with electroless nickel

Abstract

The present invention relates, generally, to methods for joining an electronic part finished with nickel and an electronic part finished with electroless nickel, which can prevent a brittle fracture, more particularly, to a method for joining an electronic part finished with nickel and an electronic part finished with electroless nickel with a solder by controlling the composition of the solder to prevent a brittle fracture occurring at the solder joining portion.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a schematic view showing a process for joining a package part finished with nickel and a printed circuit board finished with electroless Ni(P) including;

(a) forming nickel (14) on a metal wiring (12) of a BGA package (10);

(b) forming Sn-3.5Ag solder (20) on (a);

(c) forming electroless Ni(P) (22) and Sn-3.0Ag-0.5Cu solder (24) on the printed circuit board (18) to be connected with (b); and

(d) joining a BGA package finished with nickel formed in (b) and a printed circuit board finished with electroless Ni (P) by reflow process.

FIG. 2 shows the result of impact tests according to the change of contents of copper inside the lead-free solder.

(a) is a graph showing the number of impact fractures in accordance with the increase of reflow numbers when the contents of copper inside the lead-free solder changes;

(b) is a SEM photograph showing a cross-section toward PCB of a specimen passed the impact tests after the reflow in (1) if the content of copper inside the solder is 0.2 wt % in (a); and

(c) is a SEM photograph showing a cross-section toward PCB of a specimen passed the impact tests after the reflow in (1) if the content of copper inside the solder is 0.5 wt % in (a).

FIG. 3 shows a relationship between spalling behaviors of intermetallic compounds according to the kinds of solder in a printed circuit board finished with electroless Ni(P) and impact tests.

(a) is a graph showing a relationship between spalling behaviors of intermetallic compounds and the number of impact fractures at impact tests;

(b) is a SEM photograph showing a broken cross-section of Sn-3.0Ag-0.5Cu solder of which the number of impact fractures is 240 (The spalling of intermetallic compounds generates about 10% of the total length of a solder pad); and

(c) is a SEM photograph showing a broken cross-section of Sn-36.8Pb-0.4Ag solder of which the number of impact fractures is 70 (The spalling of intermetallic compounds generates about 50% of the total length of a solder pad).

Claims

1. A method of joining an electronic part finished with nickel and an electronic part finished with electroless nickel, comprising: (1) reflowing solder to a nickel portion of an electronic part finished with nickel to obtain an electronic part where an intermetallic compound and a solder are formed;(2) obtaining an electronic part finished with an eletroless nickel, of which the nickel portion is connected with the solder; and(3) solder-joining the electronic part finished with nickel obtained in the step (1) and the electronic part finished with electroless nickel obtained in the step (2).

2. The method of claim 1, wherein the electronic part is one selected from the group consisting of a semiconductor chip, a package part and a printed circuit board.

3. The method of claim 1, wherein the intermetallic compound formed on an electronic part finished with nickel is a Ni3Sn4 or (Ni,Cu)3Sn4 phase.

4. The method of claim 1, wherein the solder of the electronic part finished with nickel is a Sn—Ag—Cu series solder having the composition with 0˜10 wt % of Ag, 0˜0.4 wt % of Cu and the balance of Sn.

5. The method of claim 1, wherein the solder of the electronic part finished with electroless nickel is a Sn—Ag—Cu series solder having the composition with 0˜10 wt % of Ag, 0.1˜1.5 wt % of Cu and the balance of Sn.

6. The method of claim 1, wherein the solder of an electronic part finished with electroless nickel is Sn—Ag—Cu series solder, in case that the solder of electronic part finished with nickel is a Sn—Ag series solder; and wherein the Sn—Ag solder of the electronic part finished with nickel has the composition with 0˜10 wt % of Ag and the balance of Sn, and the Sn—Ag—Cu solder of the electronic part finished with electroless nickel has the composition with 0˜10 wt % of Ag, 0.1˜1.5 wt % of Cu and the balance of Sn.

7. The method of claim 1, wherein the solder of an electronic part finished with electroless nickel is a Sn—Ag—Cu series solder, in case that the solder of electronic part finished with nickel is a Sn—Ag series solder; and wherein the Sn—Ag—Cu solder of the electronic part finished with nickel has the composition with 0˜10 wt % of Ag, 0˜0.4 wt % of Cu and the balance of Sn, and the Sn—Ag—Cu solder of the electronic part finished with electroless nickel has the composition with 0˜10 wt % of Ag, 0.1˜1.5 wt % of Cu and the balance of Sn.

8. The method of claim 1, wherein the content of copper in the entire solder when an electronic part finished with nickel is joined with an electronic part finished with electroless nickel with solder is in 0.05 wt %˜0.4 wt %.

9. The method of claim 1, wherein the solder on an electroless nickel is reflowed again when it is joined after being reflowed before it is joined with the electronic part on the opposite side or only when it is joined with the electronic part on the opposite side.

10. The method of claim 1, further comprising: depositing a metal layer on nickel or electroless nickel.

11. The method of claim 10, wherein the metal layer is deposited with the thickness of less than 1 μm.

12. The method of claim 10, wherein the metal layer is formed of one metal selected from the group consisting of gold (Ag), silver (Ag), palladium (Pd), Organic Solderability Perservative (OSP), tin (Sn) and tin alloy.