JPH09232734A - Bump-formed flexible printed circuit board and manufacturing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a flexible printed circuit having high reliability of the connection to circuit elements such as ICs. SOLUTION: A flexible printed circuit has spherical bumps 4, the surface of which is a solder layer 5 formed on a Ni layer 6 or Au layer. The bumps 4 are formed by the Cu plating, using a high concn. brightener. The Cu ion concn. is 200-250g/liter and current density is 30-50A/dm<2> to form the spherical bumps 4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flexible printed wiring board (hereinafter simply referred to as FPC) provided with spherical bumps for connecting circuit components such as ICs and a method for manufacturing the same. In particular, the present invention relates to an FPC having bumps with high connection reliability and a manufacturing method thereof.

[0002]

2. Description of the Related Art Conventionally, bumps for connecting circuit components such as ICs are provided with an opening for exposing a circuit at a predetermined position of a resist layer provided on the surface of an FPC, and copper is plated on the opening. It has been formed by applying solder plating.

[0003]

In the conventional plating method, the plating surface was flat or was deformed to form a recess, which did not form a spherical shape properly and the connection reliability was not sufficient. Further, since the copper plating and the solder plating are in direct contact with each other, brittle copper and tin compounds are formed by heating or the like, which also hinders the reliability of connection.

[0004]

[Means for Solving the Problems] When copper plating is applied, spherical bumps are formed by increasing the copper concentration and the brightener concentration and increasing the current density. Further, in order to prevent direct contact between copper and tin, a nickel plating layer was provided on the copper plating, and a solder layer was provided thereon. In addition, a gold plating layer was provided on the nickel layer and a solder layer was provided on the nickel layer, and bumps were formed by nickel plating instead of copper plating, and the solder layer was provided thereon. With the spherical bumps thus obtained, circuit parts such as IC and F
The reliability of the connection with the PC has improved. In particular, the solder plating layer provided on the gold layer or the nickel layer so as not to come into direct contact with copper did not produce brittle copper and tin compounds even when heat was applied, so that the connection reliability was further improved.

[0005]

EXAMPLES The present invention will be described with reference to examples. An acrylic or epoxy photosensitive printing resist layer was provided on the circuit-formed flexible printed circuit board, and an opening of 0.14 mmφ was formed so that the circuit was exposed at a predetermined position. Bumps were formed in the openings by copper plating.

Conditions for Copper Plating Composition of Plating Solution CuSO ₄ : 200 ± 5 g / liter Brightening agent A ^* : 25 ± 5 cc / liter Brightening agent B ^** : 10 ± 1 cc / liter H ₂ SO ₄ : 110 ± 5 g / liter l Cl ^-: 50 ± 10ppm ^* brightener A: "Copper Cream A" (Rironaru trade name) ^** brightener B: "Copper Cream B" (Rironaru trade name) energizing conditions bath temperature: 30 to 35 ° C. Current density: 30 to 50 A / dm ² Energization time: 10 to 15 minutes

Under the above plating conditions, as shown in the figure, a spherical bump having a lower diameter of 180 to 220 μmφ and a height of 50 to 70 μm could be formed. The plating started from the periphery of the opening due to the edge effect, but the plating speed was adjusted by the brightening agent, and since the Cu ions were large and the current density was high, the plating grew upward and became a spherical bump.

The copper bumps thus obtained were further plated to form the next bump. 20 ± 5 μm solder layer provided directly on copper bumps 3-6 μm nickel layer provided on copper bumps, 20 ± 5 μm solder layer provided on it 3-6 μm nickel on copper bumps Layer, followed by a 0.025 to 0.1 μm gold plated layer, and a solder layer of 20 ± 5 μm on it

[0009]

As described in the present application, the concentration of the brightening agent is increased and Cu
With the spherical bumps obtained by increasing the ion concentration and the current density, the FPC circuit and circuit components such as ICs can be reliably connected, and the connection reliability is improved.

By heating and melting the solder layer on the bump surface, the circuit components such as IC and the FPC circuit can be connected easily and surely. This is an effect of forming substantially spherical bumps by the method of the present application.

Similar to each of the bumps described above, connection was easy and reliable, but was particularly excellent in terms of long-term reliability. That is, even when a heating test (eg, heating at 100 ° C. for 2 weeks) as an accelerated test for long-term use was performed, no decrease in bonding strength was observed at all.
This is probably due to the extremely slow growth of the hard and brittle intermetallic compound.

The presence of the nickel layer or the nickel and gold layer between the copper and the solder suppresses the growth of intermetallic compounds. In particular, gold was plated very thinly on the nickel layer, which was most effective. However, it was not effective for the gold layer to be too thick. Also, instead of forming bumps by copper plating, forming bumps by nickel plating also made it possible to secure an easy and highly reliable connection.

[Brief description of drawings]

FIG. 1 is a schematic sectional view showing a bump of the present invention.

FIG. 2 shows a case where a solder layer is directly provided on a copper bump.

FIG. 3 shows a case where a nickel layer is provided on a copper bump and a solder layer is provided thereon.

FIG. 4 shows a case where a nickel layer and then a gold plating layer are provided on a copper bump and a solder layer is provided thereon.

[Explanation of symbols]

 1 ... Substrate 2 ... Circuit 3 ... Resist layer 4 ... Copper bump 5 ... Solder layer 6 ... Nickel layer 7 ... Gold plating layer

Claims (3)

[Claims] 1. A flexible printed circuit, wherein substantially spherical bumps having high connection reliability are formed in a resist opening provided on the surface of the flexible printed circuit. 2. The flexible printed circuit according to claim 1, wherein the bump surface is made of a solder layer, and the solder layer is formed on the nickel layer or the gold layer. 3. A method of forming a bump by copper plating in a resist opening provided on the surface of a flexible printed circuit, wherein a high-concentration brightening agent is used during copper plating, and a copper ion concentration of 200 to A method of manufacturing a flexible printed circuit with bumps, comprising forming spherical bumps at 250 g / liter and a current density of 30 to 50 A / dm ² .