JPH0758150A - How to mount electronic components - Google Patents

Abstract

PURPOSE:To eliminate the positional deviation of solder bumps so as to improve the workability by using trivalent alcohol having a viscosity higher than a specific value at an ordinary temperature as a soldering flux. CONSTITUTION:Trihydric alcohol having a viscosity of 1,000cps at an ordinary temperature is used as a soldering flux. For example, 1, 2, 6-hexanetriol is used as the soldering flux. Oxide films coating solder bumps on a semiconductor chip are removed by spraying a flux containing amine hydrohalide onto the bumps and heating the bumps to 300 deg.C in a nitrogen atmosphere. Then, after spraying 1, 2, 6-hexanetriol onto the solder bumps, the solder bumps are positioned at pads on a board by the conventional method and soldering are performed by passing them through a reflow furnace whose maximum temperature is set to 350 deg.C. When this method is used, the positional deviation of the solder bumps can be eliminated and the workability can be improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for mounting electronic parts, especially semiconductor chips, which prevent misalignment. Due to the necessity of rapidly processing a large amount of information, the information processing apparatus has been made large in capacity, and the semiconductor device which constitutes the main body of the apparatus has been made large in capacity by miniaturizing the unit elements, and LSI and V
Large-capacity elements such as LSI have been put to practical use. As a method for mounting these semiconductor elements, a bare semiconductor element that is not packaged is used in place of the Jewal inline package that has a hermetically sealed structure or the flat package structure because it is necessary to downsize the device. .

[0002]

2. Description of the Related Art As a method of mounting a semiconductor element (hereinafter, semiconductor chip) on which solder bumps are formed in a matrix, flux is first applied to the solder bump formation surface of the chip by a spray method or the like, and this is applied to a ceramic multilayer circuit board. After aligning with a pad on which a pattern is formed in advance, the circuit is connected by heating the pad through an electric furnace.

The size of the solder bump is about 10 in diameter.
Many of them have a height of 0 μm and a height of about 80 μm.
They are arranged in a matrix with a pitch interval of approximately μm, but after such semiconductor chips are mounted on a circuit board, the mutual interval is necessarily 80 μm or less, so the flux is thoroughly washed and removed. It is impossible to do so, and flux often remains.

In general, amine hydrohalide is used as the flux, and this flux separates hydrogen halide, for example, hydrochloric acid (HCl) by heating,
As a result, solder fusion is performed by dissolving and removing the oxides on the surfaces of the solder bumps and pads. Then, after the soldering process is completed, conventionally, cleaning is performed using a cleaning agent such as trichloroethane. However, if the cleaning is insufficient and the amine hydrohalide remains, there is a problem that the corrosion of the solder progresses.

Therefore, recently, a fluxless joining method using no flux has been put into practical use. The method is to apply flux to the solder bumps of the semiconductor chip before soldering, then heat up to the melting point of the solder or higher to decompose and dissolve the oxide film and impurities on the surface of the solder bumps for cleaning treatment. After cleaning the surfaces of the solder bumps by carrying out the solder bumps, the semiconductor chips are aligned with the pads patterned on the circuit board and heated in an inert atmosphere for soldering. However, the problem with this method is that it tends to cause misalignment due to vibration.

[0006]

There is a fluxless bonding method as a method of mounting a semiconductor chip having a structure in which solder bumps are formed in a matrix shape on a circuit board. After the surface of the solder bumps is cleaned, the circuit board of the circuit board is cleaned. Bonding is performed by aligning with the pad and heating. However,
The diameter of the solder bump is as small as about 100 μm, which is about 250 μm.
Since they are arranged in a matrix with a fine pitch of m,
Even if you carefully align the pads on the circuit board,
Misalignment is likely to occur due to slight vibrations and impacts, which reduces workability in mass production processes. Therefore, improvement of this workability is an issue.

[0007]

[Means for Solving the Problems] The above problem is to apply a trihydric alcohol having a viscosity of 1000 cps or more at room temperature to the bonding surface of a solder bump that has been cleaned in advance, and then heat it by aligning it with the pad of the circuit board. However, it can be solved by adopting a fusion method.

[0008]

[Function] The present invention has a viscosity of 10 as a solder flux at room temperature.
It uses a trihydric alcohol of 00 cps or more. The inventor has a thixotropic (Th
Since a harmless flux with ixotropy) and self-consistency is required, a material suitable for this is studied. That is, in order to perform soldering by a method suitable for mass production, it is necessary to use a reflow method in which an object to be soldered is placed on a conveyor and passed through an electric furnace, but in this process, some shock or vibration is applied to the object. This is unavoidable and therefore requires the use of a flux that absorbs or cushions shocks and vibrations.

Here, the requirements for the flux used for this purpose are that the viscosity is high, that it evaporates or decomposes near the soldering temperature, but no corrosive gas is generated at that time. Therefore, the inventor chose trihydric alcohol as a material suitable for this. That is, it was presumed that polyhydric alcohols, especially trihydric alcohols, which do not contain any of these components, are suitable in order to generate no corrosive gas during decomposition.

That is, there are various polyhydric alcohols such as dihydric alcohol, trihydric alcohol, tetrahydric alcohol, pentahydric alcohol and hexahydric alcohol, and dihydric alcohol (glycol, a typical one is ethylene glycol). ) Has a low viscosity and a low boiling point (197.6 ° C), so it cannot be used as a flux for this purpose. Also, tetravalent,
Both pentahydric and hexahydric alcohols are crystalline solids and are not suitable for this purpose.

Trihydric alcohol (commonly known as triol)
There are various types of glycerin [CH ₂ OHCH (OH) CH ₂ O
H] decomposes as it reaches the boiling point at 290.5 ° C, while the viscosity is 1412 cps at room temperature (20 ° C). Hexanetriol [HOCH ₂ CH (OH) CH ₂ (CH ₂ ) ₂ CH ₂ OH] has a viscosity of 2584 cps at room temperature (20 ° C).
H ₂ CH ₂ CH (OH) CH ₂ OH] also has a similar viscosity and has a property of decomposing as the boiling point is reached.

According to the present invention, the flux remains in the vicinity of the soldering temperature as described above to prevent the positional deviation. By using triol for this purpose, the positioning between the solder bump and the pad is ensured and the soldering process is performed. The workability of is improved.

[0013]

[Example] Example 1: (Example of using 1,2,6-hexanetriol as a flux) A semiconductor chip has a diameter of 100.
21 μm and 80 μm high solder bumps at 250 μm pitch
21 pieces were used which were arranged in a matrix.
Here, the solder has a composition of Pb-5% Sn, the melting point is 300 ° C, and the solder bumps are made by plating. The circuit board used for mounting is made of glass ceramic, and the pad used for mounting is gold (Au) / nickel (Ni) / titanium / by vacuum deposition.
(It is made by taking a four-layer structure of Ti / chrome (Cr).

First, a solder bump of a semiconductor chip was sprayed with a commercially available flux containing an amine hydrohalide salt and heated to 300 ° C. in a nitrogen (N ₂ ) atmosphere to form an oxide film on the solder bump. Excluded. Next, after spraying 1,2,6-hexanetriol on the solder bump surface of this semiconductor chip, the solder bump of the semiconductor chip is positioned on the pad of the circuit board by the same method as the conventional method, and the maximum temperature is 350
Soldering was performed by passing it through a reflow furnace set at ° C. As a result, the solder bumps were not displaced, and no flux remained. Example 2: (Example of using 1,2,4-butanetriol as the flux) Used as the flux in Example 1,
Except that 1,2,4-butanetriol was used in place of 2,6-hexanetriol, the procedure was exactly the same.As a result of soldering, there was no displacement of solder bumps, and there was no flux residue. Was not recognized.

[0015]

As a result of implementing the present invention, the displacement of the solder bumps is eliminated, and the workability in the soldering process can be improved.

Claims (1)

[Claims] 1. A mounting method in which solder bumps of an electronic component in which solder bumps are formed in a matrix are aligned with respective pads that are pre-patterned on a circuit board and heated to perform solder joining, A method of mounting an electronic component, which comprises applying trihydric alcohol to a bonding surface of a solder bump that has been cleaned in advance, aligning it with a pad of a circuit board, heating and fusing.