JP2979880B2 - Composite lead frame and method of manufacturing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a composite lead frame for a resin-sealed semiconductor device and a method of manufacturing the same.

[0002]

2. Description of the Related Art Outer leads are made of metal lead frames,
For example, various types of composite lead frames having a copper or copper alloy lead frame or the like, and an inner lead formed by a flexible wiring board having a fine wiring pattern of a conductor formed on an insulating film have been proposed. However, in either structure, it is necessary to electrically connect the inner lead of the flexible wiring board and the outer lead 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 joining of the outer lead and the inner lead is performed under pressure and heating, but the temperature of the heating tool is 3
At a high temperature of 40 ° C. or higher, the resin (eg, polyimide resin) constituting the insulating layer or the adhesive (eg, epoxy resin-based adhesive) used for bonding the insulating layer and the inner lead is deteriorated by heating. Oxidation or carbonization undesirably results in impaired insulation and reduced strength.

When lead-tin solder is used for the purpose of joining the outer lead and the inner lead, its eutectic point (melting point: 183)
° C) is low, the above problem does not occur, but a wire bonding step performed at around 200 ° C after joining the outer lead and the inner lead, or
Because of the presence of a resin sealing step performed at around ° C, stable bonding between the outer lead and the inner lead cannot be obtained.

Further, when the bonding layer between the outer lead and the inner lead is a two-element alloy of gold and tin, the bonding strength at the bonding portion is low, and the bonding strength after heating is largely reduced.

On the other hand, the use of a commonly used gold-tin alloy having a tin content of 20% by weight involves a tool temperature exceeding 340.degree. C. and a high temperature of 380.degree. C. to 540.degree.

[0007]

Thus, according to the present invention, the outer lead and the inner lead are stably bonded to each other in the wire bonding step and the resin sealing step, and the resin and the adhesive of the insulating layer are not thermally deteriorated. It is intended to provide a lead frame and a manufacturing method thereof.

[0008]

According to the present invention, the outer leads are formed by a copper or copper alloy lead frame, and the inner leads are formed by a flexible wiring board in which a fine wiring pattern of a conductor is formed on an insulating film. In the composite lead frame, the bonding layer between the outer lead and the inner lead is made of an alloy of tin, gold and copper, and the gold content of the alloy is 10 to 40% by weight and the copper content is 10 to 40% by weight. A composite lead frame is provided.

Further, according to the present invention, there is provided a method for manufacturing a composite lead frame in which outer leads are made of copper or a copper alloy, and inner leads are made of a flexible wiring board having a fine conductor pattern formed on an insulating film. The joint surface of the outer lead is plated with tin, and the joint surface of the inner lead is plated with gold. Then, the two joint surfaces are subjected to a temperature of 200 ° C. to 500 ° C. and a pressure of 100.
g / lead to 600 g / lead for 0.5 seconds to 20 seconds under pressure and heat for bonding.

The thickness of tin plating applied to the bonding surface of the outer leads is 1.5 to 7.5 μm, and the thickness of gold plating applied to the bonding surface of the inner leads is 0.3 to 6.0 μm.
m, it is preferable that the joining thickness of the two joining surfaces is 1 to 5 μm.

Here, the flexible wiring board is 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 wiring board). 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 this sense, there is no structural change, so that it is used as the flexible wiring substrate herein.

The most important feature of the present invention is that the bonding between the inner lead of the flexible wiring board and the outer lead of the metal lead frame has a gold content of 10 as a bonding layer.
-40% by weight, copper content of 10-40% by weight gold-tin-
The use of copper alloy, such a specific alloy,
Shows high bonding strength and excellent heat resistance.

Hereinafter, the present invention will be described in detail. When bonding the inner lead of the flexible wiring board and the outer lead of the metal lead frame, first, the bonding surface of the inner lead is gold-plated, but it is more preferable that gold plating is performed after nickel plating is performed thereon It is. 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 temperature of the heating heater is set to 300 to 500 ° C., and the heating temperature is set to 0.5 to 0.5 while applying a pressure of 100 to 600 g to the lead.
Heat for 20 seconds.

By such a heating means, the tin of the outer lead plating is melted, and gold of the inner lead plating and copper of the outer lead are diffused into the molten tin, so that an alloy layer of tin, gold and copper is formed. . The gold content of this alloy layer is 10
~ 40 wt%, copper content is 10-40 wt%,
Such a composition is achieved by appropriately adjusting the amount of gold plating, the amount of tin plating, and the bonding thickness. Normally, plating is performed so that the ratio of the amount of gold plating to the inner lead and the amount of tin plating to the outer lead falls within the above range, and the bonding is performed so that the bonding thickness also falls within the above range.

The gold plating on the inner leads is usually 0.3 to 6.0 μm in thickness, preferably 0.5 to 2.0 μm.
The plating is performed so as to have a thickness of 0.1 to 0.5 μm. The plating of tin on the outer leads is usually performed to a thickness of 1.5 to 7.5 μm. The bonding thickness is suitably from 1 to 5 μm, preferably from 1 to 2 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.

One embodiment of the composite lead frame of the present invention will be described with reference to FIGS.

The metal lead frame used in the composite lead frame of the present invention is made of copper or a copper alloy and has a tie bar 13 from which outer leads 15 (15a, 15b) extend toward the vicinity of the center of the tie bar 13. Has been established.

At the center of the tie bar 13 of the lead frame, a flexible multilayer wiring board 17 (hereinafter referred to as "multilayer wiring board") is arranged.
On the upper side, an insulating film layer 19 made of, for example, polyimide
And a conductor layer 21 for grounding or power supply made of copper, for example, on the lower side. The insulating film layer 19 may use a polyimide film with a copper foil on one side (that is, the upper side).

This copper foil is later etched to form inner leads 27. The insulating film layer 19 has a ground or 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. This multilayer wiring board 17
The inner lead 27 is formed by etching or depositing copper on the copper foil adhered to the upper surface of the insulating film layer 19. A good conductor such as gold is plated on a tin-nickel base, for example, on the inner end of the inner lead 27 so that a good wire bonding connection is made. As described above, if gold plating is also applied to the inner lead end of the inner lead for wire bonding with the semiconductor element electrode, as described above, when the outer lead and the inner lead are pressurized and heated and joined together, Applying gold plating to the inner 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 1
A good conductor such as gold is also plated on the hole 23 of, for example, a tin-nickel base.

The electrical connection between the outer leads 15b of the metal lead frame and the inner leads 27 of the multilayer wiring board 17 is achieved by the above-mentioned method by heating and pressing.

In this figure, as the outer leads 15 of the metal lead frame, the leads extending from, for example, the vicinity of the four corners of the tie bar 13 are used as grounding or power supply outer leads 15a, and the others are used as signal outer leads 15b. . Outer lead for signal 1
5b is connected to the inner lead 27 as described above, but is connected to the ground or power supply lead 15a.
Are directly grounded to the conductor layer 21. For this grounding, first, the corners of the conductor layer 21 exposed from the notches of the insulating film layer 19 are also plated with gold, and the outer leads 15
Similarly to b, the tip of a tin-plated grounding or power supply lead 15a is applied to the tip and heat-pressed to form a bonding layer (gold-tin-copper alloy) 31 to be connected to the conductor layer 21 for grounding or power supply. And the conductive lead 15a. In FIG. 3, gold is plated on the upper part of the inner lead 27,
FIG. 4 is a cross-sectional view before the joining in which the lower part of the outer lead 15 is plated with tin, while FIG. 4 is a cross-sectional view after the pressure joining, and reference numeral 37 denotes a joining made of an alloy of tin, gold, and copper. Numeral 38 is a fillet discharged by pressure-heating bonding.

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 or power supply hole 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 of the present invention may be such that the flexible wiring board has a single-layer structure, that is, the structure without 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.

[0026]

EXAMPLE (Example) First, using a copper alloy having a thickness of 0.15 mm, a tie bar 13 as shown in FIGS.
Then, the outer lead 15 is manufactured. Here, the pitch at the tip of the outer lead 15 is 0.37 mm. Next, a grounding or power supply hole 23 is formed in the polyimide insulating film layer 19 having a thickness of 0.05 mm.
A two-layered multilayer wiring board 17 to which a copper alloy foil having a thickness of 2 mm is adhered is manufactured. A copper foil having a thickness of 0.018 mm is attached to the multilayer wiring board 17 and etched to form inner leads 27 having a pitch of 0.12 mm, and the outer ends of the inner leads 27 are plated with gold / nickel. 2.0 μm, nickel: 0.5 μm) The outer leads 15 b are tin-plated (tin: 7.5 μm) on the outer ends, and the signal leads 15 b of the outer leads 15 are used as a tool (heater).
Under pressure and heat. Here, the plating ratio of gold and tin is 26% by weight for gold and 74% by weight for tin.

Each condition in the joining was as follows. Temperature: 320 ° C. Pressure: 400 g / lead Time: 10 seconds The alloy composition of the formed bonding layer 37 was 25% by weight of Au and 35% by weight of copper.

On the other hand, gold / nickel plating is applied to the multilayer wiring board 17, and tin-plated grounding or power supply outer leads 15a are connected by pressure and heat bonding to connect the composite lead frame of the present invention. Produced.

The inner lead 27 and the outer lead 15 (15) of the composite lead frame thus obtained
No appearance of carbonization or oxidation of the polyimide resin or adhesive near the joints of (a, 15b) was observed.

Inner lead 27 and outer lead 15
In order to confirm that the bonding strength with (15a, 15b) was stable, the peel strength of the bonding portion was measured.
Even after standing at 0 ° C. for 1000 hours, there was almost no change from the initial value at about 90 gf / piece.

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

FIG. 5 shows the relationship between the copper composition of the joint and the peel strength. The weight ratio of tin to gold at the joint is 6
5/35. When copper is not included, the peel strength is low,
In the case of 10 to 40% by weight of copper, the peel strength increases,
When the content is more than the weight%, the material becomes brittle and the peel strength is reduced.

FIG. 6 shows that the composition of the joint is tin: 40% by weight,
25% by weight of gold and 35% by weight of copper, and 62% by weight of tin and 38% by weight of gold and not containing copper at 175 ° C.
The change in peel strength when heated up to 000 hours is shown. Those containing no significant decrease in peel strength by heating, whereas those containing copper showed little decrease in peel strength after heating.

[0034]

According to the present invention, the inner lead and the outer lead are stably bonded even when subjected to the wire bonding step and the resin sealing step, and the bonding temperature of the both is low. A composite lead frame free from thermal deterioration of the resin or adhesive to be obtained is obtained.

Further, according to the present invention, since the outer leads are made of copper or a copper alloy, the outer leads are plated with tin and the inner leads are plated with gold, and are simply heated and joined at a predetermined pressure and temperature. Easy and stable bonding strength and highly reliable bonding can be 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 the relationship between the copper content at the joint of the composite lead frame and the peel strength.

FIG. 6 is a graph showing a change in peel strength of a joint including copper and a joint not including copper after heating.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Lead frame 13 Tie bar 15a Outer lead for grounding or power supply 15b Outer lead for signal 17 Flexible multilayer wiring board 19 Insulating film layer 21 Conductive layer for grounding or power supply 23 Hole for grounding or power supply 27 Inner lead 31 Gold-tin- Copper alloy layer 33 Semiconductor element 35 Bonding wire 37 Gold-tin-copper alloy layer 38 Fillet discharged by pressure bonding

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Masaharu Takagi 3-1-1, Sukekawa-cho, Hitachi City, Ibaraki Prefecture Inside the wire plant of Hitachi Cable Co., Ltd. (72) Inventor Tomio Murakami Hitachi City Assistant, Ibaraki Prefecture 3-1-1 Kawamachi Inside the cable plant of Hitachi Cable Co., Ltd. (56) References JP-A-4-199668 (JP, A) JP-A-2-244650 (JP, A) (58) Fields surveyed (Int .Cl. ⁶ , DB name) H01L 23/50

Claims (3)

(57) [Claims] 1. A composite lead frame in which an outer lead is constituted by a copper or copper alloy lead frame and an inner lead is constituted by a flexible wiring board in which a fine wiring pattern of a conductor is formed on an insulating film. The bonding layer with the lead is made of an alloy of tin, gold and copper, and the gold content of the alloy is 10 to 4
A composite lead frame, wherein the composite lead frame has 0% by weight and a copper content of 10 to 40% by weight. 2. A method of manufacturing a composite lead frame, wherein the outer leads are formed by a copper or copper alloy lead frame, and the inner leads are formed by a flexible wiring board having a fine wiring pattern of a conductor formed on an insulating film. Tin plating is applied to the joint surface of the outer lead, and gold plating is applied to the joint surface of the inner lead.
0.5 seconds to 20 at 100 g / lead to 600 g / lead
A method for manufacturing a composite lead frame, comprising: applying pressure and heating for two seconds; 3. The thickness of tin plating applied to the bonding surface of the outer leads is 1.5 to 7.5 μm, and the thickness of gold plating applied to the bonding surface of the inner leads is 0.3 to 6. 0μ
3. The method of manufacturing a composite lead frame according to claim 2, wherein the bonding thickness of the two bonding surfaces is 1 to 5 μm.