JPH11345896A - Circuit board - Google Patents

Abstract

(57) [Problem] To provide a circuit board capable of improving the bondability between an electroless nickel plating film and an electroless palladium plating film and increasing the bonding strength of a bump. An electroless nickel plating film, an electroless palladium plating film, and an electroless gold plating film are formed on an external connection terminal portion in this order, and a bump is formed on the plating film. It is characterized in that the electrolytic palladium plating film has a phosphorus content of 0.001 to 1 wt%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a circuit board having bumps formed on external connection terminals, such as a package for a BGA (ball grid array) type semiconductor device.

[0002]

2. Description of the Related Art In a package for a BGA type semiconductor device, a required plating film is formed on an external connection terminal portion, and a bump such as a solder bump is formed on the plating film. In general, the above-mentioned plating film is generally formed of an electroless nickel film and an electroless gold plating film thereon, but recently, cost reduction has been required, and an alternative metal to gold has been required. An electroless palladium plating film has been applied. In this case, the electroless nickel plating film, electroless palladium plating film, or the electroless nickel plating film, electroless palladium plating film, electroless gold plating film (thin) as the base of the bump Is adopted. In the case of electroless palladium plating, various reducing agents are used. When a phosphate-based reducing agent is used, the plating film contains phosphorus. When using trimethylamine borane as a reducing agent, boron is contained in the plating film,
This plating bath has hardly been put to practical use.

[0003]

In the case of the above-mentioned package for a semiconductor device, the bonding property between the bump and the underlying plating film becomes a problem. VPS (Vaper Phase)
There is a heating test called Solder). This is temperature 220
A sample is put in a solvent vapor at a temperature of ° C., and the bump bonding strength after heating for a certain period of time is observed. When severe conditions are given in this heating test, there is a problem that it is difficult to obtain the required bonding strength of bumps in the case of forming an electroless palladium plating film using the above hypophosphite as a reducing agent.

[0004] As a result of the inventor's intensive study, the peeling of the bump is not the peeling between the bump and the underlying plating,
A phenomenon occurred between the electroless nickel plating film and the electroless palladium plating film, and a phenomenon in which the electroless nickel plating film was partially exposed after the test was found. Therefore, as a result of various studies, the inventors have focused on the phosphorus content in the electroless palladium plating film, and found that the bondability between the base plating films can be improved by keeping the phosphorus content lower than before. That is, the object of the present invention is:
It is an object of the present invention to provide a circuit board capable of improving the bondability between an electroless nickel plating film and an electroless palladium plating film and increasing the bonding strength of a bump.

[0005]

The present invention has the following arrangement to achieve the above object. That is, in the circuit board according to the present invention, an electroless nickel plating film and an electroless palladium plating film are formed in this order on the external connection terminal portion,
In the circuit board having bumps formed on the electroless palladium plating film, the electroless palladium plating film has a phosphorus content of 0.001 to 1 wt%. As described above, by reducing the phosphorus content in the electroless palladium plating film, the bondability between the electroless nickel plating film and the electroless palladium plating film could be improved. When the phosphorus content was zero, the required joining strength could not be obtained.

In the circuit board according to the present invention, an electroless nickel plating film, an electroless palladium plating film, and an electroless gold plating film are formed in this order on the external connection terminals,
In a circuit board having bumps formed on the electroless gold plating film, the electroless palladium plating film has a phosphorus content of 0.001 to 1 wt%. The electroless gold plating film is provided as a protective film for the electroless palladium plating film, and may be thin in terms of cost. Further, the electroless gold plating film diffuses into the solder bumps, and the bonding property between the bump and the electroless palladium plating film is good. Then, by setting the phosphorus content in the electroless palladium plating film within the above range, the bondability between the two plating films was improved as described above.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 shows a package 10 for a BGA type semiconductor device as an example of a circuit board. Reference numeral 12 denotes a resin substrate. On one side of the resin substrate 12,
A wiring pattern 14 and a chip mounting portion 16 are formed. The wiring pattern 14 and the chip mounting portion 16 are formed by etching a copper foil. On the other surface side of the resin substrate 12, a wiring pattern (external connection terminal) electrically connected to the wiring pattern 14 via the through-hole via 18
20 are formed.

A plating film described later is formed on the wiring pattern 20, and the wiring pattern 2 is formed through the plating film.
On bumps 0, bumps 22 such as solder bumps are formed. 24
And 26 are masks made of solder resist.
A semiconductor chip (not shown) is mounted on the chip mounting portion 16, the semiconductor chip and the wiring pattern 14 are electrically connected by wires, and the semiconductor chip and the wires are sealed with a sealing resin to form a semiconductor. Used as a device.

An electroless nickel plating film and an electroless palladium plating film are formed on the wiring pattern 20 in this order. Alternatively, an electroless gold plating film is further formed. Electroless nickel plating film is for corrosion resistance, 5μ
m. The electroless palladium plating film is used to improve the bondability with a bump such as a solder bump, and is formed to have a thickness of about 0.3 μm. The electroless gold plating film is for protecting the electroless palladium plating film, and may be as thin as about 0.05 μm.

The electroless nickel plating solution used may be a commercially available known one. Also, the electroless gold plating solution may be a commercially available substitution type known solution. As the electroless palladium plating solution, a plating solution having a basic composition of palladium chloride as a metal source, phosphite as a reducing agent, and an organic acid having a mercapto group as a stabilizer was used. By using phosphite as the reducing agent, the phosphorus content in the electroless palladium plating film deposited could be suppressed lower than that using a conventional hypophosphite. That is, while the phosphorus content when using hypophosphite is 4 wt% or more, when using phosphite, 1 wt%
The following phosphorus content was able to be reduced. The phosphorus content is proportional to the amount of phosphite added.

The following is an example of the bath composition of the electroless palladium plating solution. Palladium chloride 0.01 mol / L Ethylenediamine 0.08 mol / L Sodium phosphite 0.02 mol / L Thiodiglycolic acid 30 mg pH 6 Bath temperature 60 ° C

[0012]

EXAMPLES In the following examples, the ball shear strength was measured using a commercially available ball shear tester.
In the evaluation, when the solder balls were mounted on the board and then heated once, twice, and three times by the VPS device, the sample was heated once, twice, and three times by the VPS device before mounting the solder balls. Was measured.
Judgment was made from the ball shear strength and the degree of exposure of the electroless nickel plating film after the ball on the substrate was peeled off after the ball shear test (20 samples). Example 1 The content of phosphorus in palladium was about 0.001% by weight.
The electroless palladium plating solution adjusted so as to be used was used. Electroless Ni 5μm / Electroless Pd 0.3μm / Electroless Au 0.05mμ
A BGA substrate having a plating configuration of m was prepared, and a ball shear test was performed. The results are shown in Tables 1 and 2.

[0013]

[Table 1]

[0014]

[Table 2]

Example 2 An electroless palladium plating solution was used in which the content of phosphorus in palladium was adjusted to about 0.5% by weight. A BGA substrate having a plating configuration of electroless Ni 5 μm / electroless Pd 0.3 μm / electroless Au 0.05 μm was prepared, and a ball shear test was performed. The results are shown in Tables 3 and 4.

[0016]

[Table 3]

[0017]

[Table 4]

Example 3 An electroless palladium plating solution adjusted so that the phosphorus content in palladium was about 1.0% by weight was used. A BGA substrate having a plating configuration of electroless Ni 5 μm / electroless Pd 0.3 μm / electroless Au 0.05 μm was prepared, and a ball shear test was performed. The results are shown in Tables 5 and 6.

[0019]

[Table 5]

[0020]

[Table 6]

Comparative Example 1 An electroless palladium plating solution prepared by using formate as a reducing agent so as to prevent phosphorus from being eutectoid in palladium was used.
A BGA substrate having a plating configuration of electroless Ni 5 μm / electroless Pd 0.3 μm / electroless Au 0.05 μm was prepared, and a ball shear test was performed. The results are shown in Tables 7 and 8.

[0022]

[Table 7]

[0023]

[Table 8]

Comparative Example 2 An electroless palladium plating solution prepared by using hypophosphite as a reducing agent and adjusting so that about 5% of phosphorus was eutectoid in palladium was used. Electroless Ni 5μm / Electroless Pd 0.3μm / Electroless Au
A BGA substrate having a plating configuration of 0.05 μm was prepared, and a ball shear test was performed. The results are shown in Tables 9 and 10.

[0025]

[Table 9]

[0026]

[Table 10] As is clear from Tables 1 to 6, when the phosphorus content in the electroless palladium plating film is 0.001 to 1.0 wt%, the ball shear strength is high irrespective of whether or not there is a heat history, and the film is peeled off. On the other hand, peeling occurred in the state where the solder remained, that is, in the solder bumps, no peeling occurred between the electroless nickel plating film and the electroless palladium plating film, and the bonding strength between both plating films was improved.

On the other hand, as shown in Tables 7 to 10, the phosphorus content in the electroless palladium plating film was zero,
Alternatively, in the case of about 5 wt% or more, as can be seen from the fact that the ball shear strength is relatively lower than that of the above-described embodiment and the underlying electroless nickel plating film is exposed, the electroless nickel plating film and the electroless palladium plating It can be seen that the bondability with the film is low.

In the above embodiment, the three-layer plating of electroless nickel plating, electroless palladium plating, and electroless gold plating is described. However, the two-layer plating of electroless nickel plating and electroless palladium plating is employed. However, exactly the same results were obtained. The circuit board according to the present invention is not limited to a package for a BGA type semiconductor device, but can be applied to a circuit board in which a bump is formed on an external connection terminal portion.

[0029]

According to the circuit board of the present invention, as described above, the phosphorus content in the electroless palladium plating film is reduced so that the distance between the electroless nickel plating film and the electroless palladium plating film is reduced. Can be improved, and the bonding strength of the bump can be increased.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a package for a BGA type semiconductor device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Package 12 Resin board 14 Wiring pattern 16 Chip mounting part 18 Through-hole via 20 Wiring pattern (terminal for external connection) 22 Bump 24, 26 Mask

Claims (2)

[Claims] An electroless nickel plating film and an electroless palladium plating film are formed on an external connection terminal in this order, and a bump is formed on the electroless palladium plating film. Has a phosphorus content of 0.0
A circuit board, wherein the content is 0.01 to 1 wt%. 2. A circuit board in which an electroless nickel plating film, an electroless palladium plating film, and an electroless gold plating film are formed in this order on an external connection terminal portion, and a bump is formed on the electroless gold plating film. Phosphorus content of the electroless palladium plating film is 0.0
A circuit board, wherein the content is 0.01 to 1 wt%.