JP2533220B2 - Semiconductor device soldering method and device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Outline] With respect to soldering of semiconductor devices and the like, it is an object of the present invention to provide a highly reliable soldering method and device. When performing solder joining in a soldering device, a vaporizing method is characterized in that the inside of the vapor soldering device is preliminarily set to an inert gas atmosphere and then the working liquid is evaporated to perform vapor soldering processing. And also a vapor phase soldering container,
It is characterized by having a heater part for heating the working fluid, a cooling means for cooling the evaporated working fluid, an air supply port communicating with the container for supplying an inert gas, and an exhaust port for exhausting the inside of the container. Configure soldering equipment.

[Industrial applications]

The present invention relates to a soldering method and device for semiconductor devices and the like.

Since it is necessary to process a large amount of information at high speed, information processing devices are being made larger in capacity, and semiconductor devices, which are the main components of this information processing device, are being made smaller and larger in capacity, and LSI and V
Integrated circuits such as LSI have been put to practical use. Here, in the conventional integrated circuit, unit elements mainly consisting of transistors are formed in a matrix on a semiconductor chip (hereinafter abbreviated as a chip) consisting of a few millimeters square, and the bonding pads are provided around the chip. The circuit is connected.

Then, after the chip is mounted on the ceramic circuit board by using an adhesive or a eutectic alloy, circuit connection is performed by a method such as wire bonding to a pad which is pre-patterned on the circuit board.

However, for large-capacity elements such as LSI, the wire bonding method is difficult due to the downsizing of pads and the high density of pad intervals. Instead, the solder bumps are arranged in a matrix on the chip surface. The flip-chip method has been adopted in which this is aligned with a large number of pads of a conductor line provided on the uppermost layer of a multilayer ceramic circuit board and directly welded.

[Conventional technology]

Generally, most of the chips on which LSIs and VLSIs are formed are 10 mm square or less, and a large number of solder bumps are formed in a matrix on the chips.

However, the size of this bump is 200 μm in diameter and 1 in height.
Extremely small, around 00 μm.

Here, the solder bumps are formed by using indium (In), tin 37% lead alloy (Sn-37% Pb), Pb-5% Sn, etc. using a vacuum deposition method, a solder hole method, a plating method, or the like. There is.

On the other hand, as a circuit board on which a semiconductor chip is mounted, a multi-layer ceramic circuit board in which glass ceramic or the like is used as a dielectric and copper (Cu) is used as a conductor is often used.

That is, via holes (Via) are formed at the circuit connection positions in the thickness direction of a plurality of green sheets made of glass ceramics.
After forming a (-hole), a conductor pattern such as a conductor line is printed and a via hole is filled by using a screen printing method, laminated and integrated, and then baked to form a circuit board. A fine pad made of Cu is formed at the chip mounting position on the circuit board thus formed, and a thin film of platinum (Pt) / gold (Au) or the like is formed on this by a vacuum deposition method or the like. In some cases, the bumps are patterned, and solder bumps to which solder is attached are formed on the semiconductor bumps, similarly to the above semiconductor chip.

Here, the reason for forming a layer structure with Pt / Au / solder on the Cu pad is that the solder easily forms a solid solution with Cu, and Pt / Au / solder
This is to prevent so-called solder erosion from occurring due to intervening.

In order to securely mount the semiconductor chip on the bumps provided on the circuit board, it is necessary to use flux in the normal soldering, and conventionally, the semiconductor chip in which flux is applied to the solder bumps is used on the circuit board. It was performed by heating the solder bumps above the melting point of the solder while being accurately aligned with the solder bumps.

However, since the flux contains activators such as chlorine compounds and bromine compounds, if the flux remains after soldering, the active components contained in the flux will cause solder joining. There is a problem that parts are corroded.

Therefore, soldering using a vapor phase soldering equipment (VPS equipment) is recommended as a special soldering method that does not use flux for mounting this type of semiconductor chip.

FIG. 1 is a sectional view showing the construction of an embodiment of the VPS device according to the present invention, but there is no difference from the conventional one except for the sealed container 1.

That is, the VPS device is composed of a VPS container 2 for soldering and a heater section 3 for heating the VPS container 2.

The VPS container 2 has a detachable first lid 4 on the upper part thereof, and a wire 6 for suspending a holder 5 is provided below the first lid 4, and a chip aligned with a bump of a circuit board 18 is attached to the holder 5. 7 is placed.

Further, a cooling mechanism for wrapping the side surface of the VPS container 2 is provided on the upper part of the VPS container 2 so that the water 9 circulates. Also, VP
At the bottom of the S container 2, a fluorocarbon 10 having a boiling point adjusted to a soldering temperature is contained as a working liquid.

As a soldering method, when the heater portion 3 is energized to heat the carbon fluoride 10 and water is circulated in the cooling mechanism 8, the carbon fluoride 10 reaches a predetermined boiling point and starts boiling. While being vaporized, the vapor of carbon fluoride reaches the cooling mechanism 8 at the upper part of the container, radiates heat of condensation at this place to be liquefied, and then hangs down along the container and returns to the liquid retainer.

In this state, the circuit board 18 on which the semiconductor chip 7 is placed is placed on the holder 5, and the first lid 4 that hangs this is hung down. Due to the condensation heat of the carbon fluoride vapor, the semiconductor chip 7 and the circuit board 18 are
Are heated and soldered.

During this time, since the inside of the container is replaced with the vapor of carbon fluoride, the solder bumps on the bonded portion are in a state of being shielded from the air.

Then, the soldering work is completed by pulling up the first lid 4 and taking out the circuit board 18.

However, even if soldering work is performed using such a VPS device, good soldering is not always performed.

2 and 3 show the soldering condition observed by a stereoscopic microscope. FIG. 2 shows a good condition and FIG. 3 shows a bad condition.

That is, when the first solder bumps 11 on the semiconductor chip 7 side and the second solder bumps 12 on the circuit board 18 are joined and heated in the VPS device as shown in FIGS. A good one due to fusion is a soldered ball 13 having a drum-shaped cross section as shown in FIG. 2 (B), but some of them are shown in FIG. 3 (B). The first solder bump 11 and the second solder bump 12
There is a case where there is a joint with the streak 14 between the and, there is a high contact resistance because it is not integrated, and since it is not completely contact, it is necessary to solve from the viewpoint of reliability. It was

[Problems to be Solved by the Invention]

When soldering a semiconductor chip with a flip chip type terminal structure to a circuit board using a VPS device,
Both solder bumps are not necessarily spherical and may be welded with streaks at the joint.

Then, this invention aims at the proposal of the vapor phase soldering method which does not produce the above-mentioned adhesion failure, and the proposal of the improved soldering apparatus.

[Means for solving the problem]

The purpose of the above is to make the inside of the vapor-phase soldering device into an inert gas atmosphere in advance when the soldering is performed in the vapor-phase soldering device containing a working liquid which becomes a heating medium by evaporation. This can be solved by a soldering method characterized by vaporizing a liquid and performing a vapor phase soldering process. Further, according to the present invention, there is provided a vapor phase soldering container for carrying out such a soldering method, a heater section for heating the working liquid contained in the container, and a cooling means for cooling the evaporated working liquid. Further, there is provided an improved soldering device characterized by having an air supply port communicating with the container for supplying an inert gas and an exhaust port for exhausting the inside of the container.

[Action]

The present invention has been made as a result of investigating the cause of the cross-sectional shape of the solder joint showing a streaky twisted shape as shown in FIG. 3 (B) when the conventional VPS device is used for soldering. Is.

That is, the streaks 14 are formed by the oxide generated by the oxidation of the solder, and the chip having the first solder bumps 11 is aligned with the second solder bumps 12 provided on the circuit board. Put in vapor phase soldering equipment, VPS
It was found that it occurs during the process of performing.

That is, in FIG.
When the carbon fluoride 10 at the bottom of the S container 2 is heated, the inside of the container should be filled with carbon fluoride vapor, and the air inside should be expelled and disappear, but in reality some air remains. And this oxidizes the surface of the solder burp,
It was found that incomplete joining occurred as shown in FIG. 3 (B).

Therefore, according to the present invention, as shown in FIG. 1, the entire VPS device is put in a sealed container 1 having a second lid 15 and an inert gas is supplied from an air supply port 16 and exhausted from an exhaust port 17 while soldering. Oxygen (O ₂ ) in the VPS container is shut off by performing the soldering work. By adopting such a method, soldering failure can be eliminated.

〔Example〕

In the VPS apparatus having the structure shown in FIG. 1, the VPS container 2 is made of Pyrex glass, and carbon fluoride having a boiling point of 230 to 260 ° C. is used as the carbon fluoride (working liquid) 10.

 This carbon fluoride is a mixture of plural kinds having different boiling points.

The wire 6 hanging from the first lid 4 and the holder 5 are made of stainless steel, and the diameter of the wire 6 is 1 mm.

Nitrogen (N ₂ ) was used as the inert gas to be supplied to the sealed container 1, and the gas was supplied from the air supply port 16 at a rate of 5 / min.

In this way, soldering was performed in the same manner as in the conventional method except that the entire VPS container 2 was placed in an N ₂ atmosphere. As a result, the yield in the soldering process was about 80% in the conventional method. The bumps were integrated to form solder balls, and could be improved to 100%.

 FIG. 4 is a graph showing the effect of the present invention.

In FIG. 4, (A) shows the relationship between the joining temperature and the joining rate when the VPS device is soldered in the air by the conventional method, and (B) shows the VPS device placed in a nitrogen atmosphere for soldering. The relationship between the bonding temperature and the solder bump bonding rate in the case of performing is shown, and the shaded area in the figure represents the area of good bonding.

 The solder used was indium solder.

In FIG. 4 (A), the reason why the bonding rate decreases when the bonding temperature becomes too high is that the oxidation of residual oxygen in the air and the surface of the solder bump is promoted as the temperature becomes higher. It is thought that it is 100 in any case
It is difficult to obtain a bonding rate of%.

On the other hand, as is apparent from FIG. 4 (B), according to the method of the present invention, a bonding rate of about 100% is achieved at a temperature of 200 ° C. or higher.

It should be noted that the present invention is not limited to the embodiment, and the point is that the inside of the VPS device is placed in an inert atmosphere and then VPS is performed. Further, the supply port and the exhaust port for the above-mentioned inert gas may be indirectly connected to the VPS through the sealed container as described above, or may be directly provided in the VPS container itself.

Further, in the present embodiment, the bonding when the solder bumps of both the semiconductor chip and the circuit board are provided is described, but the present patent is applicable to the bonding when the solder bumps are provided on only one of them.

〔The invention's effect〕

By carrying out the present invention in which the soldering is performed in an inert atmosphere, it is possible to eliminate the oxidation of the solder during the soldering, and thus it is possible to eliminate the occurrence of defects and perform highly reliable soldering.

[Brief description of drawings]

FIG. 1 is a sectional view showing the structure of a VPS device according to the present invention. FIG. 2 is a sectional view showing a good soldering state. FIG. 3 is a sectional view showing a bad soldering state. 3 is a graph showing the relationship between temperature and solder bump bonding rate according to the method of FIG. In the figure, 1 is a sealed container, 2 is a VPS container, 3 is a heater part, 4 is a first lid, 5 is a holder, 6 is a wire, 7 is a semiconductor chip, 8 is a cooling mechanism, 10 is carbon fluoride, and 15 is A second lid, 16 is an air supply port, 17 is an exhaust port, and 18 is a circuit board.

 ─────────────────────────────────────────────────── ─── Continuation of front page (56) References JP-A-61-242097 (JP, A) JP-A-2-152246 (JP, A)

Claims (4)

(57) [Claims] 1. When performing a solder joint in a vapor phase soldering apparatus containing a working liquid which is vaporized and becomes a heating medium, the vapor phase soldering apparatus is preliminarily made to have an inert gas atmosphere before the operation. A soldering method comprising vaporizing a liquid and performing a vapor phase soldering process. 2. The soldering method according to claim 1, wherein the vapor phase soldering apparatus is placed in an inert atmosphere so that the inside of the vapor phase soldering apparatus is made an inert atmosphere. 3. A vapor-phase soldering container, a heater section for heating the working liquid contained in the container, and a cooling means for cooling the evaporated working liquid, further comprising an inert gas in communication with the container. A soldering device having an air supply port for supplying and an exhaust port for exhausting the inside of a container. 4. A vapor-phase soldering container is installed in another sealed container, and the sealed container is provided with a supply port for supplying the inert gas and an exhaust port. Item 3
The described soldering device.