JP3846948B2 - Bare chip mounting parts - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to a bare chip mounting resin substrate and a bare chip mounting component using the same.
[0002]
[Prior art]
Recently, a bare chip called “flip chip” is known in which a semiconductor chip is not included in a package and is mounted on a substrate as it is in order to meet a demand to pack many functions on a substrate having a limited area. . Metal pads (projections) are formed on the bare chip pads (electrodes) instead of the leads, and the bumps are bonded to the pads (electrodes) formed on the surface of the substrate by heat treatment.
[0003]
There are printing methods, vapor deposition methods, plating methods, etc. as methods for forming pads on the surface of the substrate. However, with the recent miniaturization of wiring patterns, fine pattern accuracy cannot be obtained with printing methods, and vapor deposition methods are also available. However, because of the cost, the plating method is currently used. In addition, electroless plating methods that do not require conduction are the mainstream. As conventional electroless plating, autocatalytic solder plating is generally used in order to obtain connection strength with the bump on the bare chip side.
[0004]
[Problems to be solved by the invention]
However, even such an autocatalytic electroless solder plating method is difficult to apply when the substrate is formed of a resin. That is, when a bare chip is mounted on a resin substrate, the resin substrate has a larger coefficient of thermal expansion (about 5 times) than the semiconductor bare chip, and a large stress is generated between the bare chip and the substrate. Therefore, in order to relieve this stress, it is necessary to form a thick bump on the bare chip and a pad on the substrate to ensure a sufficient distance between the bare chip and the substrate. In solder plating, it is difficult to form a thick film while maintaining fine pattern accuracy. The bumps on the bare chip side can be electroplated, so it can be formed thick enough, but the electroless plating to form the pads on the substrate side maintains a fine pattern with high precision when forming thinly. Although it can be formed, when it is formed thick, the precision of the fine pattern is inevitably lowered.
[0005]
The present invention pays attention to such a conventional technique, and provides a resin substrate for mounting a bare chip that can surely relieve stress and a bare chip mounting component using the same.
[0006]
[Means for Solving the Problems]
In the resin substrate of the present invention, a first electroless plating film of 20 μm or more is formed on the surface with an autocatalytic electroless plating solution selected from the group consisting of copper, copper alloy, nickel and nickel alloy. A second electroless plating film is formed on the electroless plating film with a substitutional electroless plating solution selected from the group consisting of gold, gold alloy, silver, silver alloy, tin, and tin alloy.
[0007]
Here, the “substrate” is a generic term for all things on which a bare chip can be mounted, such as a package, in addition to a substrate in a general sense.
[0008]
If a self-catalyzed electroless plating solution selected from the group of copper, copper alloy, nickel, nickel alloy is used, even if the substrate is made of resin, the fine pattern as a “pad” is maintained while maintaining a fine pattern of 20 μm or more. A thick first electroless plating film can be formed. This is because the catalytic activity in electroless plating such as copper and nickel is higher than that of conventional electroless solder plating.
[0009]
Further, a second electroless plating film is formed on the first electroless plating film with a substitutional electroless plating solution selected from the group of gold, gold alloy, silver, silver alloy, tin, and tin alloy. Therefore, the required bonding strength between the first electroless plating film (pad) and the bare chip bump can be obtained.
[0010]
The thickness of the second electroless plating film may be a thickness that can reliably bond the bump of the bare chip and the first electroless plating film of the resin substrate, for example, a thickness of about 0.1 to 20 μm. good.
[0011]
Nickel is preferable as the counter metal of the “copper alloy” forming the first electroless plating film, and tin is preferable as the counter metal of the “nickel alloy”.
[0012]
Furthermore, tin is preferred as the partner metal of the “gold alloy” for forming the second electroless plating film, bismuth is preferred as the partner metal of the “silver alloy”, and the partner metal of the “tin alloy” is Indium is preferred.
[0013]
The bump of the bare chip is formed by electrolytic plating with a kind of electrolytic plating solution selected from the group of gold, silver, copper, platinum, palladium, tin, indium, and their respective alloys. The electrolytic plating film for forming the bump is formed with a thickness of 20 μm or more. In the case of electrolytic plating, it is easier to form a thicker film than in the case of electroless plating on the substrate side. The reason why gold, silver, copper, platinum, palladium, tin, indium, and their respective alloys are used as the bump forming metal is that they have excellent electrical characteristics and good bonding properties.
[0014]
The bare chip bumps thus formed are placed on the second electroless plating film of the resin substrate and bonded by heat treatment. The mounting component on which the bare chip is mounted in this way ensures a sufficient distance between the bare chip and the resin substrate. Therefore, even if stress due to the difference in thermal expansion coefficient occurs between the resin substrate and the bare chip. The stress can be surely relieved.
[0015]
【Example】
An electroless copper plating film (first electroless plating film) as a “pad” was formed on the surface of the substrate using a self-catalyzed electroless copper plating solution on a resin substrate made of epoxy. .
[0016]
The electroless copper plating solution used was PB-570 (trade name) in the Interplate process of EBARA Eugene Corporation. Using this electroless copper plating solution, a fine pattern was formed on the resist-patterned substrate. An electroless copper plating film was formed.
[0017]
The thickness of the electroless copper plating film was 30 μm, and the precision of the fine pattern as the “pad” was maintained.
[0018]
Then, the electroless copper-plated resin substrate is immersed in substitutional tin plating, and only on the fine pattern of the electroless copper plating film, an electroless tin plating film (second electroless film) as a “bonding layer”. (Plating film) was formed. The thickness of the obtained electroless tin plating layer was 12 μm.
[0019]
The electroless tin plating solution has the following composition and conditions.
・ Methanesulfonic acid …………………………… 100ml / l
・ Stannous chloride …………………………………… 45g / l
・ Thiourea ……………………………………… 100g / l
・ Bath temperature ……………………………………………… 70 ℃
・ Time ……………………………………………… 3 hours 【0020】
Next, an electrolytic gold plating film as a “bump” was formed on a flip-chip metal pad as a “bare chip” using a gold electrolytic plating solution. The thickness of the obtained electrolytic gold plating film was 20 μm.
[0021]
The electrolytic gold plating solution used was Microfab Au100 (trade name) manufactured by Nippon Electroplating Engineers.
[0022]
The flip chip on which the bump was formed was mounted on the resin substrate, and the bump of the flip chip and the electroless tin plating film of the substrate were joined by heat treatment. Heating was performed in the atmosphere using a flux R5003 (trade name) manufactured by Nippon Alpha Metals Co., Ltd., at a heating temperature of 230 ° C. and a heating time of 3 minutes.
[0023]
The distance between the flip chip and the substrate bonded in this way is as much as 40 μm, and the stress caused by the difference in thermal expansion coefficient between them can be surely alleviated.
[0024]
【The invention's effect】
According to the present invention, a sufficient distance can be ensured between the bare chip and the resin substrate, and even if a stress due to a difference in thermal expansion coefficient is generated between the resin substrate and the bare chip, the stress is reliably ensured. Can be relaxed.

Claims (1)

On the bare chip pad, bumps of 20 μm or more are formed with a kind of electrolytic plating solution selected from the group of gold, silver, copper, platinum, palladium, tin, indium, and their respective alloys.
On the surface, a first electroless plating film of 20 μm or more is formed with an autocatalytic electroless plating solution selected from the group consisting of copper, copper alloy, nickel, and nickel alloy, and the first electroless plating film is formed on the first electroless plating film. Mounted on a bare chip mounting resin substrate on which a second electroless plating film is formed with a substitutional electroless plating solution selected from the group consisting of gold, gold alloy, silver, silver alloy, tin, and tin alloy,
The second electroless plating film of the resin substrate and the bump of the bare chip are joined by heat treatment,
A bare chip mounting component characterized in that a distance that can relieve stress caused by a difference in thermal expansion coefficient between a bare chip and a resin substrate is secured .