JP2846181B2 - Manufacturing method of composite lead frame - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a composite lead frame for a semiconductor device of a resin sealed type.

[0002]

2. Description of the Related Art Various types of composite lead frames having an outer lead formed of a metal lead frame and an inner lead formed of a flexible wiring board having a fine wiring pattern of a conductor formed on an insulating film have been conventionally proposed. However, in either structure, it is necessary to electrically connect the inner leads of the flexible wiring board and the outer leads on the outer frame side by some method. Since the inner leads from the flexible wiring board are laminated on the insulating layer (usually a polyimide film), the following problems occur in joining.

[0003] That is, the bonding between the outer lead and the inner lead is performed under pressure and heat. When the temperature of the heating tool is higher than 340 ° C, a resin (for example, a polyimide resin) constituting the insulating layer or the insulating layer is used. The adhesive (for example, epoxy resin adhesive) used for bonding the inner lead and the inner lead is deteriorated by heating, and is oxidized or carbonized, thereby deteriorating insulation properties and decreasing strength.

When Pb-Sn solder is used for the purpose of joining the outer lead and the inner lead, its eutectic point (melting point: 1
83 ° C.), the above problem does not occur, but a wire bonding step performed at about 200 ° C. after joining the outer lead and the inner lead, or
Since there is a resin sealing step performed at around 00 ° C., stable bonding between the outer lead and the inner lead cannot be obtained.

On the other hand, when a commonly used Au-Sn alloy having a Sn content of 20% by weight is used for joining, the tool temperature exceeds 340.degree. C. and is as high as 380 to 540.degree. .

[0006]

Thus, the present invention provides:
A composite lead frame that stably joins the outer leads and inner leads withstands the wire bonding process and the resin sealing process, and has no thermal deterioration in the resin or adhesive of the insulating layer
The purpose is to provide a manufacturing method.

[0007]

According to the present invention, there is provided a composite lead frame comprising an outer lead formed by a metal lead frame and an inner lead formed by a flexible wiring board having a fine wiring pattern of a conductor formed on an insulating film. In a method for manufacturing a composite lead frame in which the outer lead and the inner lead are joined by a gold-tin eutectic alloy method, a tin plating having a thickness of 4.0 to 8.0 μm is applied to a joint surface of the outer lead and the inner lead is provided. Gold plating having a thickness of less than 0.5 to 1.0 μm is applied to the bonding surface of the first and second surfaces, and then the two bonding surfaces are heated and bonded by a gold-tin eutectic alloy method, whereby the bonding layer is substantially formed of tin and gold. Consisting of only an alloy layer of which the gold content in the alloy layer is 10 to 10.
A method for producing a composite lead frame is provided, wherein the alloy layer is 40% by weight.

Here, the flexible wiring board refers to a so-called flexible wiring board in which a fine wiring pattern of a conductor is formed on an insulating film (including a tape-shaped one). What is called a TAB tape is also a flexible material in which a fine wiring pattern of a conductor is formed on an insulating film, and in that sense, there is no structural change, so that it is used as a flexible wiring substrate herein.

The most important feature of the present invention is that an Sn-Au alloy having a gold content of 10 to 40% by weight is used as a bonding layer in bonding an inner lead of a flexible wiring board and an outer lead of an outer frame. However, such a specific alloy has an appropriate melting point range (210-305 ° C.) and, because there is no phase composed of AuSn, which is a brittle intermetallic compound, can be used at a high temperature of 340 ° C. or more in joining. Heating is unnecessary and stable bonding is achieved.

Hereinafter, the present invention will be described in detail.

When joining the inner lead of the flexible wiring board and the outer lead of the outer frame, first, the joining surface of the inner lead is gold-plated. This is a preferred embodiment. Then, tin plating is applied to the joint surface of the outer lead.

As the heating means used for bonding, known heating means such as infrared beam heating and heating by a heater are employed, but a heating method using a heater is preferred. When a heating heater is used, the heating temperature is set to 300 to 500 ° C. and 0.5 to 20 while applying a pressure of 31 to 94 g to the lead.
Heat for 2 seconds.

By such a heating means, tin diffuses into gold, and as a result, an alloy layer of tin and gold is formed. The gold content of the alloy metal is 10 to 40% by weight. Such a composition can be achieved by appropriately adjusting the gold plating amount and the tin plating amount. Normally, plating is performed such that the ratio of the amount of gold plating to the inner leads and the amount of tin plating to the outer leads falls within the above range.

The thickness of gold plating on the inner lead
Is preferably performed so as to have a thickness of 0.5 to less than 1.0 μm, and nickel plating is usually performed to a thickness of 0.1 to 1.5 μm.
Is performed to have a thickness of The plating of tin on the outer lead is usually performed so as to have a thickness of 1.5 to 7.5 μm.

The plating method of gold, tin or nickel is performed by a method known per se, for example, an electroplating method. For gold plating, semi-bright plating using a neutral or acidic bath is employed. For tin plating, matte plating using a sulfuric acid bath or a fluoridation bath is employed.

FIG. 1 shows an example of the composite lead frame of the present invention.
This will be described with reference to FIG.

The lead frame has an outer frame 13 from which outer leads 15 (15a, 15b) extend toward the vicinity of the center of the outer frame 13.

At the center of the outer frame 13 of the lead frame, a flexible multilayer wiring board 17 (hereinafter referred to as "multilayer wiring board") is arranged. Layer 19;
On the lower side, there are two layers, for example, a grounding and power supply conductor layer 21 made of copper.

The direction of the insulating film layer 19 is single-sided (i.e., upper surface) Dohakuzuke polyimide film.

This copper foil is later etched to become inner leads. The insulating film layer 19 has a grounding and power supply hole 23 opened by press punching or the like. The conductor layer 21 is adhered to the insulating film layer 19 with an adhesive or the like. The inner leads 27 are formed by, for example, etching or depositing a copper foil attached to the upper surface of the insulating film layer 19 of the multilayer wiring board 17. At the inner tip of this inner lead 27,
A good conductor such as gold is plated on a Sn—Ni base, for example, so that a good wire bonding connection can be made. If gold plating is also applied to the inner tip of the inner lead for wire bonding as described above, when the outer lead and the inner lead are joined by the gold-tin eutectic alloy method in the present invention as described above, The use of gold plating on the lead side is very convenient in terms of plating work because each of the gold plating operations can be performed simultaneously. The above multilayer wiring board 17
The conductor layer 21 exposed from the hole 23
A good conductor such as gold is plated on an n-Ni base.

Outer lead 15 of the lead frame
The electrical connection between b and the inner leads 27 of the multilayer wiring board 17 is achieved by the heat and pressure bonding by the method described above.

In this figure, the outer leads of the lead frame are extended from, for example, the four corners of the outer frame 13 as the outer leads 15a for grounding and power supply, and the others are used as the outer leads 1 for signal.
5b. The signal outer lead 15b is connected to the inner lead 27 as described above, but the ground and power supply lead 15a is connected to the conductor layer 21b.
To ground directly. For this ground, first, more bumps are formed on the gold plating on the corners of the conductor layer 21 exposed from the notches of the insulating film layer 19, against the distal end of the ground to the bump and the power supply lead 15a, the heating Crimping to form a bonding layer (Sn-Au alloy) 31 and a conductor layer 21
And the ground and power supply lead 15a.

A semiconductor element 33 is mounted on such a multilayer lead frame, and a bonding wire 35 is provided between a signal terminal of the semiconductor element 33 and a plating terminal of the inner lead 27.
And the semiconductor element 3
A bonding wire 35 connects between the ground terminal 3 and the portion of the conductor layer 21 that is exposed from the ground and power supply holes 23 of the multilayer wiring board 17. Finally, the semiconductor device can be manufactured by resin sealing so as to wrap the inner leads 27.

The structure of the composite lead frame according to the present invention may be such that the flexible wiring board has a single layer other than that described above, that is, does not have the conductor layer 21 shown in FIG. Further, a conductor layer may be further laminated with a structure having a conductor layer for grounding and a conductor layer for power supply.

[0025]

EXAMPLE ( Experimental Example ) First, an outer frame 13 and an outer lead 15 as shown in FIGS. 2 and 3 are manufactured using a 0.15 mm thick Fe-42% Ni alloy. Here, outer lead 1
The pitch at the tip of No. 5 is 0.37 mm. Next, a grounding and power supply hole 23 is formed in a 0.05 mm thick polyimide insulating film layer, and a 0.10 mm thick 42 alloy (F) is formed on one surface of the polyimide insulating film layer.
An e-42% Ni alloy) foil is bonded to produce a two-layer multilayer wiring board 17. The multilayer wiring board 17 has a thickness of 0.01
An 8 mm copper foil is adhered and etched to form inner leads 27 having a pitch of 0.12 mm.
7 was plated with Au / Ni (Au: 2.0
μm, Ni: 0.5μm), the outer end of the inner lead 27, Sn plated (Sn: 7.5μ
m) The signal lead 15b of the outer lead 15 is heated and pressed by a tool (heater). Here, the ratio of the plating amount of Au to Sn is 26% by weight of Au,
Is 74% by weight. Reference numeral 37 denotes an Au / Sn junction layer.

The conditions for joining were as follows.

Temperature: 320 ° C. Pressure: 40 g / lead time: 10 seconds The alloy composition of the resulting bonding layer 37 was 15% Au.

On the other hand, the hole 2 of the multilayer wiring board 17
Au / Ni plating was performed on the conductor layer 21 exposed from No. 3, and the Sn-plated grounding and power supply outer leads 15a were connected by heat and pressure bonding to produce the present composite lead frame.

No appearance of carbonized or oxidized polyimide resin or adhesive near the joint between the inner lead and the outer lead of the composite lead frame thus obtained was observed.

The peel strength of the joint was measured for the purpose of confirming that the joint strength between the inner lead and the outer lead was stable. The initial value was about 45 gf / mm even after being left at 150 ° C. for 1000 hours. There was little change.

A series of experimental results will be described for a better understanding of the present invention.

FIG. 3 is a cross-sectional view before bonding in which gold is plated on the upper part of the inner lead 27 and tin is plated on the lower part of the outer lead 15, while FIG. 4 is a cross-sectional view after pressure bonding. Reference numeral 37 denotes a joining layer made of an alloy of tin and gold.

The total plating thickness of gold and tin is fixed (7.5 μm).
In the case of m), as shown in FIG. 5, the thickness of the Au / Sn junction cross section tended to increase as the Au plating thickness increased. This is because the Au layer which does not react when the thickness of gold is large because the temperature at the time of pressure bonding is low remains as it is. The presence of such an Au layer is merely due to the thickness of the bonding layer.
Not only is disadvantageous for the joining structure, but also
In terms of consumption, it is preferable from the viewpoint of economy and workability.
It is not good.

On the other hand, when the thickness of the gold plating is constant at 1.0 μm, as shown in FIG. 6, the thickness of the junction cross section is substantially constant (4.0 μm) regardless of the tin plating thickness , Rather
Conversely, the thicker the tin plating thickness, the lower the tendency .

Next, focusing on the tensile strength of the joint, as shown in FIG. 7, the Au plating thickness is 0.5-2.0 μm ,
Preferably, a region having the highest tensile strength was present at a place of less than 0.5 to 1.0 μm . Also, the thickness of Au plating
When the thickness is fixed at 0.1 μm, the tin plating thickness is 4.
There was a region having a large tensile strength at a thickness of 0 to 8.0 μm (see FIG. 8).

FIG. 9 shows a quantitative analysis of the joints and plots the relationship with the plating thickness. Referring to FIG. 7, the region having a large tensile strength has a gold content of 10 to 40% by weight. It is understood that this is a function of the alloy composition.

Au- consisting of an alloy having a gold content of 20% by weight
FIG. 1 shows that the Sn junction was analyzed by X-ray diffraction.
A diffraction pattern such as 0 was obtained, and no brittle intermetallic compound represented by AuSn was generated. AuSn was not formed in the alloy of 10% by weight of gold or the alloy of 40% by weight of gold.

On the other hand, for the purpose of a reliability test of a joint made of an alloy of gold and tin, the composition of the treated joint subjected to a high-temperature storage test at 150 ° C. was Sn-10 wt% Au-Sn-40 wt%
In the Au range, no decrease in peel strength was observed even after 1000 hours. An example is shown in FIG. In addition, a temperature cycle test (-30 ° C x 30 minutes hold⇔150
(Holding at 30 ° C. for 30 minutes) was carried out for 1,000 cycles, but no peeling occurred and there was almost no decrease in peel strength.

[0039]

According to the method of the present invention, the method used for the insulating layer
Composite lead frame without thermal degradation of resin and adhesive
In addition to being easily obtained, when the inner lead and the outer lead are joined by the gold-tin eutectic alloy method, gold plating having a thickness of 0.5 to less than 1.0 μm is applied to the inner lead side. When gold plating is applied to the inner tip of the same inner lead for securing, not only can these gold plating operations be performed simultaneously, etc., but also the gold-tin alloy layer without the Au layer remains. This has the effect that a sound bonding layer can be easily obtained.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating an example of a composite lead frame according to the present invention.

FIG. 2 is a plan view illustrating an example of a composite lead frame according to the present invention.

FIG. 3 is a cross-sectional view showing a state before joining an inner lead and an outer lead.

FIG. 4 is a cross-sectional view showing a state after the inner lead and the outer lead are joined.

FIG. 5 is a graph showing a change in the thickness of the bonding cross section when the Au plating thickness and the Sn plating thickness are changed.

FIG. 6 is a graph showing a change in the thickness of the bonding cross section when the Au plating thickness is fixed and the Sn plating thickness is changed.

FIG. 7 is a graph showing the strength of the bonding layer when the Au plating thickness and the Sn plating thickness are changed.

FIG. 8 is a graph showing the strength of the bonding layer when the Au plating layer is fixed and the Sn plating thickness is changed.

FIG. 9 is a graph showing the composition of an Au / Sn junction layer.

FIG. 10 is a diagram showing an X-ray diffraction pattern of a bonding layer.

FIG. 11 is a graph showing the heat resistance of the strength of the Au / Sn junction.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Lead frame 13 Outer frame 15a Outer lead for grounding and power supply 15b Outer lead for signal 17 Flexible multilayer wiring board 19 Insulating film layer 21 Grounding and power supply conductor layer 23 Grounding and power supply hole 27 Inner lead 31 Bump 33 Semiconductor Element 35 Bonding wire 37 Sn-Au alloy layer 38 Hillet discharged by pressure bonding

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Shoji Takagi 3-1-1, Sukekawa-cho, Hitachi-shi, Ibaraki Pref. Inside the cable plant of Hitachi Cable (72) Inventor Hiroki Tanaka 3550 Kida Yomachi, Tsuchiura-shi, Ibaraki Hitachi Cable, Ltd. System Materials Research Laboratory (72) Inventor Kenji Yamaguchi 3550, Kida Yomachi, Tsuchiura City, Ibaraki Prefecture Hitachi Cable, Ltd. System Materials Research Laboratory (56) References JP-A-62-232948 (JP, A) JP-A-3-142286 (JP, A)

Claims (1)

(57) [Claims] (1) Connect the outer leads to the metal lead frame.
The inner lead on the insulating film.
Flexible wiring board with fine wiring pattern
The outer lead of the composite lead frame configured as
And the inner lead are joined by a gold-tin eutectic alloy method
In the manufacturing method of the composite lead frame
The plating surface of the board is tin-plated with a thickness of 4.0 to 8.0 μm.
In addition, the thickness of the inner lead joint surface is 0.5 to 1.0.
Apply gold plating of less than μm, then heat both joint surfaces
Bonding by the gold-tin eutectic alloy method
The layer consists essentially of an alloy layer of tin and gold, wherein
To form an alloy layer having a gold content of 10 to 40% by weight
A method for manufacturing a composite lead frame, comprising: