JP2615149B2 - IC chip mounting method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Application of the Present Invention" The present invention relates to a printed circuit board,
A method of mounting IC chips using a method of precision printing electrical wiring on an insulating substrate such as a glass substrate or a substrate having an insulating surface.

"Prior art" Conventionally, to form electric wiring on a printed circuit board, a copper foil is pasted on an insulating substrate such as glass epoxy, and the electric wiring is formed by a wet etching method using a known photolithography process. Had to be taken.

In the case of a device such as a thermal head, a conductive metal centering on Au is deposited on a ceramic substrate, which is an insulator, over the entire substrate surface by an ion plating method or the like,
As in the case of a printed circuit board, a method of forming an electric wiring by a wet etching method using a photolithography method has been adopted.

On printed circuit boards, etc., the pin spacing between the holes for the terminals of the semiconductor element is 0.1 inch (2.45 mm), and the pattern formation on the high-density printed wiring board, in which three or more electrical wiring circuits are drawn, is exclusively formed by photolithography. Method was used. A method has been adopted in which a dry film is attached to a printed wiring board, a wiring pattern is drawn on the dry film by photographic techniques of exposure and development, and an unnecessary portion is dissolved with a solvent to form the pattern.

The material cost of the copper foil, dry film, developer and the like used in this method is expensive, and the exposure apparatus is also expensive, which has contributed to increase the manufacturing cost.

Furthermore, the photolithography method requires a complicated process and requires a considerable amount of time, and this method itself has led to high costs.

In addition, a photolithography process is also used when forming an electrode pattern for a thermal head, an image sensor, and a liquid crystal display device, which increases the manufacturing cost of each device.

In order to solve such a problem, by directly forming on a substrate by a printing method, a material cost of a copper foil, a photoresist, a developing solution and the like required as a wiring base and a time required for the process required in the conventional method and There have been proposed methods of reducing labor costs and reducing costs.

An insulating layer is formed on an insulating substrate such as glass, glass epoxy, or ceramic, or a substrate on which wiring is already provided. A conductive printing ink containing metal powder or mixed metal powder is formed on the insulating layer by a printing method to about 1 to 20 μm. Is to print a pattern having a film thickness of

COB (chip-on-board) technology is known for mounting an IC for driving an electronic device on a circuit drawn directly on a substrate by such a method.
The C electrode pad and the signal input / output part of the circuit on the substrate were connected one by one using a thin metal wire.

However, a flip chip method has been developed in which bumps are provided on IC pads to directly contact signal input / output portions of a circuit on a substrate due to demands such as productivity and cost.

In this case, the contact between the IC bumps and the signal input / output portion of the circuit on the substrate is not completely made, causing a problem that a conduction failure occurs and a product yield is reduced.

The invention of the present application has a structure in which a signal input / output portion of a circuit on a substrate is subjected to press processing at least on a portion of the circuit formed by electrodes or leads drawn directly on the substrate by a printing method or the like so as to contact the bump of the IC. After adjusting the height of the IC, the IC bump is brought into contact with the signal input / output part of the circuit on the board to make the electrical connection, thereby solving the above-mentioned problem, improving the product manufacturing yield and reducing the product manufacturing cost. It has an effect.

 Hereinafter, the present invention will be described by way of examples.

Example A predetermined electrode or lead pattern (2) was printed on a substrate having an insulating surface by a known screen printing method using a polymer type copper paste commercially available as a conductive printing ink.

The polymer type copper paste used in this example is commercially available from Mitsui Mining & Smelting under the trade name S-5000 and has a thickness of 5 μm.
It is made up of copper particles having a particle size of the order, an epoxy resin and an organic solvent.

Such a conductive printing paste is printed in a predetermined pattern (2) using a 200 to 400 mesh screen.
In this case, the width of the electrode or lead of the printed pattern should be at least 40μ.
m is about 100 μm at maximum, and the space between screen meshes is 20 to 40 μm. Naturally, the printed pattern (2) has a height difference corresponding to the mesh.

Now, when printing 100 linear electrodes with a thickness of 20 μm and a width of 40 μm, the maximum thickness is 27 μm and the minimum thickness is 13 μm. There was also a height difference between the electrodes. This is shown in FIG.

As described above, it is naturally impossible to bring the IC chip into contact with an electrode pattern having a height difference of about 15 μm to obtain perfect conduction.

Therefore, in this embodiment, first, the electrodes or lead patterns (2) shown in FIG. 1 were printed on the substrate (1) having an insulating surface by using the above-mentioned conductive paste. Although FIG. 1 shows only a part thereof, 80 electrode patterns were printed. In this state, the electrode or the lead pattern has a height difference as described above. For example, the height of the electrode (33) is 15 μm, the height of the electrode (3) is 29 μm, and the average of 80 electrodes is 1 μm.
It was 9.5 μm.

Next, preliminary heat treatment is performed on the printed pattern. That is, a process was performed in which heat was applied to such an extent that the conductive paste was not completely solidified to remove a part of the organic solvent present in the printed pattern. Actually, preliminary heat treatment was performed at 60 ° C. for about 5 minutes.

Next, the electrode was subjected to a press treatment. In the case of this embodiment, using a roll press at a surface pressure of 20 kg / cm ² ,
Press processing was performed on the print pattern subjected to the preliminary heat treatment. Thereafter, heat treatment was performed at 180 ° C. for 30 minutes to completely solidify the electrode pattern. At this time, the height of the electrode (33) is 14 μm, and the height of the electrode (3) is 20 μm.
The average height of the zero electrodes was 18.0 μm. FIG. 2 (b) shows the state of the electrode pattern after pressing.

This press processing may be performed only on the portion of the electrode pattern formed on the substrate (1) that is in contact with the bumps of the IC chip, but if the entire electrode pattern or almost the entire electrode pattern is performed, the electrode pattern is present in the pattern formed by the press processing. Another feature is that the contact area between the copper particles is increased, and the conductivity of the electrode is improved.

Next, the bumps (6) of the IC chip (5) and the signal input / output portion of the pattern (2) on the substrate are aligned and brought into contact.

At this time, apply an ultraviolet light curable adhesive (4) to the IC chip (5) while heating to about 150 ° C., irradiate the ultraviolet light and bond, then stop heating and mount the IC chip on the substrate. To end. The situation at this time is shown in FIG.

The adhesive (4) for bonding the IC chip (5) to the substrate expands and contracts in volume with a change in temperature. In the present embodiment, the adhesive was cured in a heated state, that is, in a state where the volume was expanded. Therefore, even if the temperature was lowered, the adhesive contracted in volume and only increased the force pressing the IC chip (5) against the substrate. It has the characteristic that it can withstand enough.

IC for print pattern without press processing for comparison
The results of mounting the chip and examining the electrical connection characteristics are shown in the table below.

In the method of the present invention thus subjected to the press treatment, all the connection parts show good conductivity, and the yield of the connection parts is 100%.
And could be.

In this embodiment, the difference between the highest and lowest electrode heights after pressing was 6 μm. Originally, it is considered that this height difference 0 shows the best result, but according to the present inventors, the height difference is 8 μm
But it turns out that it can be connected.

〔effect〕

According to the method of the present invention, the electrode patterns formed by the printing method can be formed to have the same height, and complete conduction can be obtained without any defective conduction portion when mounting the IC chip.

Another feature is that the resistance value of the electrode is reduced by the press treatment.

[Brief description of the drawings]

1 and 2 show a printed pattern of an electrode according to the method of the present invention. FIG. 3 shows how the IC chip is mounted. 1 ... substrate 5 ... IC chip 2 ... electrode pattern 4 ... adhesive

 ──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Hiroshi Yamazaki 10 examiner, Tateishi Electric Co., Ltd., Hanazono Todocho, Ukyo-ku, Kyoto-shi, Kyoto, Japan Examiner Kimikohiko Kim (56) JP-A-2-10844 (JP, A)

Claims (2)

(57) [Claims] 1. A step of printing a paste having conductive particles on a substrate having an insulating surface on a pattern of electrodes or leads by a screen printing method, and performing a pressing process on at least a portion of the printed pattern which is in contact with an IC chip. The step of making the applied height uniform, the step of performing a heat treatment on the printed pattern to complete the electrodes or leads, and the step of opposing the pads of the signal input / output sections of the electrodes or leads and the bumps of the signal input / output sections of the IC chip. Connecting the IC chip to the IC chip. 2. A preliminary heat treatment is performed on the print pattern prior to the step of performing a press process on at least a portion of the print pattern that is in contact with the IC chip to adjust the height of the electrodes or leads according to claim 1. IC chip mounting method characterized by applying