JPH08242063A - Wiring circuit board and its manufacture - Google Patents

Abstract

PURPOSE: To form an electrode of a uniform size in a proper position to be attached and detached easily by coating a hard metal which becomes a base with a soft conductive substance (solder and conductive resin) as much as required for fusing as an external connection electrode of a BGA, thus constituting the whole to be almost a ball-shape. CONSTITUTION: A hard metallic layer 11 is formed in a lower surface of a substrate 10. A bump 13 of almost a ball-shape is arranged and formed to almost a matrix form by performing patterning by means of a photoetching method. A resist pattern 12 corresponding to each bump is comprised of a peripheral part covered with a resist of a center part covered with resist - a doughnut-like opening part - doughnut-like resist. After the bump 13 consisting of a hard metal which becomes a base of an external connection electrode is formed, the lower surface of the substrate 10 is immersed in solder liquid and the bump 13 is coated with solder. Solder is formed as much as required for direct surface attaching with an external circuit and functions as a soft metallic part which contributes to connection with an external circuit.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a printed circuit board on which a semiconductor integrated circuit element (hereinafter referred to as a chip) is mounted and which is used for connecting to an external circuit.

More specifically, the present invention relates to a wired circuit board for a ball grid array type (BGA) semiconductor package.

[0003]

2. Description of the Related Art Conventionally, as a typical device for connecting a chip to an external circuit such as a printed wiring board, there is a quad flat package (hereinafter referred to as QFP).

In the QFP, inside the package, the chip and the inner lead of the lead frame are connected by wire bonding or the like, and a region including the chip is molded with resin to form a package. This is a semiconductor package in which leads are drawn, the leads are formed in a gull wing shape, and the leads are connected to an external circuit, and are most widely used.

Recently, as a new connection device, the B
GA type semiconductor packages are becoming popular.

The package relates to a leadless chip carrier which can be directly surface-mounted on an external circuit, as exemplified in Japanese Patent Laid-Open No. 59-172758. The external connection electrodes (ball-shaped solder pads) are arranged in a substantially matrix shape so that they can be directly surface-mounted.

Further, as a semiconductor package of a similar form to this, a structure in which metal pins are erected in place of the solder pads is inserted into through holes formed in the printed wiring board in advance and fixed by soldering. So-called pin grid array type (Pi-n Grid array ...
Semiconductor packages (referred to as GA) are also known.

The advantage of the BGA over the QFP lies particularly in the increased packing density, in that the area required for mounting the BGA is significantly larger than the substantial area of the external circuit board required for mounting the QFP. It's getting smaller. Also,
QF when mounting a chip with about 200 pins
In P, the terminal pitch needs to be narrowed to about 0.5 mm,
Since the terminal pitch of BGA is about 1.5 mm, it is possible to mount more highly integrated chips.

Further, unlike the lead frame, the wiring pattern can be freely designed on the printed circuit board, and it becomes easy to mount a plurality of chips on one module.

In other words, the process of semiconductor package evolution is: QFP (terminals on all sides) → PGA (terminals on bottom) → B
It can be said to be GA (the terminal is the bottom surface and thinner than PGA). This type of semiconductor device is recently becoming popular as a multi chip module (Multi Chip Module-e = MCM).

[0011]

The external connection electrode (ball-shaped solder pad) in the conventional BGA type semiconductor package has the following problems because the material is only solder.

After the package is once attached to the external circuit, the solder pad is completely deformed and contributes to fusion, so that it is difficult to replace the package.

Particularly in the semiconductor field where technological innovation is remarkable, the life cycle of the chip is short, and when the function of the electronic equipment applying it is improved (including repair), the function of replacing the package on the surface of the external circuit is provided. Required.

The conventional method of forming a solder pad is to print or drop molten solder on the electrode formation area,
It was a method of forming a ball shape by the surface tension at the time of heating (reflow).

It is difficult to provide a large number of solder pads at the correct positions and in a uniform size by printing or dropping.

The present invention has a structure in which a package can be easily attached and detached as an electrode for external connection of a BGA, and a method for forming an electrode in which each electrode can be easily formed in a correct position and in a uniform size. The purpose is to provide.

[0017]

The electrode for external connection according to the present invention does not have a structure made of only a solder material, but a soft conductive material (solder or conductive material) necessary for fusion bonding on a hard metal serving as a base. (A resinous material) is coated to form a substantially ball-shaped structure as a whole.

In the present invention, like solder,
Those that are easily melted and deformed by heating or that have low rigidity compared to the terminal part of the external circuit, such as conductive resin,
It is called "soft", and it is called "hard" if it maintains a solid state even at the solder melting temperature and its rigidity is not inferior to that of the terminal portion of the external circuit.

That is, the present invention according to claim 1 is a wired circuit board having a structure in which electrodes for external connection are arranged on the lower surface in a substantially matrix form so as to be directly surface-mounted to an external circuit. It is characterized in that the connecting electrode is formed by laminating or coating a soft conductive material on a bump made of a hard metal, and the overall shape is substantially a ball shape.

The present invention according to claim 2 is characterized in that the bump is
It is characterized in that it is made of copper, aluminum, or an alloy thereof, the conductive material is made of solder or resin, and the external connection electrode is made of a combination selected from them.

According to a third aspect of the present invention, there is provided a method of manufacturing a wired circuit board, which comprises at least the following steps when forming the external connection electrodes of the wired circuit board. (A) A step of patterning the hard metal layer formed on the lower surface of the printed circuit board to form bumps, which will be terminal portions for surface attachment to an external circuit, in a substantially ball shape. (B) A step of immersing the substrate in a liquid conductive substance that is soft in a solid state, and laminating or coating the soft conductive substance on the bumps. (C) A step of heating the conductive material into a substantially ball shape.

[0022]

Embodiments of the present invention will be described below with reference to the drawings showing the order of manufacturing steps.

As the wiring circuit board 10, a copper clad laminate (a copper foil is attached to both sides or one side of an insulating base material made of epoxy resin or the like) is used as a base material, and this is used as a photoetching method or the like. Then, the one on which the chip mounting portion and the wiring pattern are formed is used. A hard metal layer 11 (copper plating) is formed on the lower surface of the substrate 10.
(See Figure 1 (a))

In the figure, the upper surface is the chip mounting surface, and the external connection electrodes are formed on the lower surface. Inside the wired circuit board 10, the wired circuit pattern is conducted from the upper surface to the lower surface, and the pattern ends are arranged in a substantially matrix on the lower surface, but they are not shown.

The hard metal layer 11 is formed by photoetching.
Then, the bumps 13 having a cross-sectional shape (substantially ball-like) as shown in FIG. 1C are arranged and formed on the lower surface of the substrate in a substantially matrix shape.

To form the bumps 13 into a substantially ball shape by etching, a photoresist pattern is formed.
1 (b) -As shown in FIG. 1 (b) '.

Resist pattern corresponding to each bump
12 includes a central portion covered with a resist, a donut-shaped opening portion, and a peripheral portion covered with a donut-shaped resist.
(See the plan view of Figure 1 (b) ')

After the bumps 13 made of hard metal, which will be the bases of the electrodes for external connection, are formed, the lower surface of the substrate 10 is dipped in a solder solution to cover the bumps 13 with solder.

The solder may be formed in an amount necessary for direct surface mounting to an external circuit, and functions as a soft metal portion that directly contributes to joining with the external circuit.

Next, the solder is heated and melted into a substantially ball shape. (Not shown)

[0031]

In the structure of the electrode for external connection according to the present invention, since the soft metal portion directly contributing to the joining is small,
Even after the package is attached to the external circuit, it is easy to replace the package.

In addition, in the method of manufacturing an electrode for external connection according to the present invention, it is easy to provide a large number of solder pads at correct positions with a uniform size.

[0033]

[Brief description of drawings]

FIG. 1 is an explanatory view showing a method of manufacturing an external connection electrode according to the present invention in the order of manufacturing steps.

[Explanation of symbols]

 10 ... Wiring circuit board 11 ... Hard metal layer 12 ... Resist pattern 13 ... Bump (hard metal)

Claims (3)

[Claims] 1. A wired circuit board having a structure in which electrodes for external connection are arranged in a substantially matrix form on the lower surface so as to be directly surface-mounted to an external circuit, wherein the electrodes for external connection are made of a hard metal. A wiring circuit board, characterized in that the bumps are laminated or covered with a soft conductive material and the overall shape is substantially ball-like. 2. The bump is made of copper, aluminum, or an alloy thereof, the conductive material is made of solder or resin, and the external connection electrode is made of a combination selected from them. 1. The printed circuit board according to 1. 3. A method for manufacturing a wired circuit board, which comprises at least the following steps in forming an electrode for external connection of the wired circuit board according to claim 1. (A) A step of patterning the hard metal layer formed on the lower surface of the printed circuit board to form bumps, which will be terminal portions for surface attachment to an external circuit, in a substantially ball shape. (B) A step of immersing the substrate in a liquid conductive substance that is soft in a solid state, and laminating or coating the soft conductive substance on the bumps. (C) A step of heating the conductive material into a substantially ball shape.