JP3327171B2 - TAB tape with stress buffer layer and ball terminals - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal stress buffer layer and a TAB tape with ball terminals for mounting a semiconductor chip such as an LSI.

[0002]

2. Description of the Related Art Ball terminals and TAB on a printed circuit board
T-BGA (Ta) with semiconductor chip mounted via tape
In recent years, a high degree of reliability has been required for a pe ball grid array).
A temperature cycle test that simulates practical use up to a high temperature is regarded as important.

However, the thermal expansion coefficient of the printed circuit board is usually 15 to 20 PPM / ° C., whereas the thermal expansion coefficient of the silicon chip is 3 PPM / ° C.
Thermal expansion stress (thermal stress) due to the difference in thermal expansion coefficient between the ball terminals directly bonded to the printed circuit board
As a result, there is a problem that a thermal fatigue crack of the solder occurs at the interface between the printed circuit board and the ball terminals joined by the solder.

For this reason, recently, as shown in FIGS. 6 to 8, a TAB tape with a thermal stress buffer layer provided with a thermal stress buffer layer 3 made of an elastomer between a semiconductor chip 1 and a polyimide tape 2 is used. Methods for preventing thermal fatigue cracks in solder have been proposed.

[0005] As shown in FIG.
The AB tape includes a wiring pattern 4 formed by etching a copper foil and a circular land 6 formed of a solder resist 5 on one surface of the polyimide tape 2, and an elastomeric adhesive 7 on the other surface of the polyimide tape 2. And a thermal stress buffer layer 3 interposed therebetween. The thermal stress buffer layer 3 absorbs the thermal expansion stress of the semiconductor chip 1 and the printed circuit board 8 so that the ball terminals 9 made of solder balls are provided.
This is intended to prevent thermal fatigue cracks occurring in the solder portion. The wiring pattern 4 is connected to a plurality of aluminum electrode terminals 11 of the semiconductor chip 1 via a plurality of inner leads 10, 10,.

[0006]

However, such a conventional structure has various disadvantages as described below.

[0007] 1. First, in order to mount the semiconductor chip 1 on the thermal stress buffer layer 3, it is necessary to apply an adhesive 12 on the thermal stress buffer layer 3, as shown in FIG. Since the agent 12 was applied by printing or the like immediately before assembling the semiconductor chip 1, (1) the applied adhesive 12 was directly or a volatile solvent eluted from the adhesive 12 was applied to the aluminum electrode terminal 11 side of the semiconductor chip 1. It flows out and contaminates it, and the inner lead 1
Connection failure with 0 frequently occurred. (2) Since the assembling process of the semiconductor chip 1 is performed by the semiconductor assembly maker, an optimum bonding is performed according to the type of the elastomer 3 attached to the TAB tape supplied from the tape maker. The agent 12 must be selected each time, and there is an inconvenience that very troublesome management such as storage management increases. (3) In addition, a special process of print coating is required in the semiconductor assembling process, and it is necessary to enhance and improve the equipment in the conventional inner lead bonding process.

[0008] 2. Next, conventionally, since the solder ball 9 was formed at the final stage of assembly, (1)
Heating process to melt solder (230-250 ° C, 10
Second), new facilities need to be installed, and (2) package destruction due to extra heating steps, semiconductor chip 1
In some cases, voids may occur at the bonding interface between the polyimide film 2 and the polyimide film 2. (3) Also, since the formation of the solder balls 9 in the final stage of assembly is performed on a semiconductor-by-semiconductor basis, the efficiency of mounting and transporting the solder balls 9 is very poor. (4) In addition, when the formation failure of the solder ball 9 occurs, it is necessary to repair the expensive semiconductor chip 1 in order not to waste it, which further complicates the process. Was. (5) Further, when the solder ball 9 is formed in the final stage of assembly, the surface of the circular land 6 forming the solder ball 9 has already been oxidized or contaminated, and the connection is similar to the connection of the inner lead 10. In addition, many poor connections between the lands 6 and the solder balls 9 occurred. In particular, the step of connecting the inner leads 10
It is kept at 70 ° C. for several minutes, and in the sealing step with the sealing agent 13, it is kept at 170 ° C. for several hours. Copper was diffused and copper oxide was formed, resulting in the remarkable inhibition of the formation of the handball 9.
(6) The solder balls 9 are usually mounted using a flux, and the solder paste printing method requires a large amount of flux in the paste, so post-cleaning is required. Since a water-based cleaning agent containing an agent is used, moisture enters the package during this cleaning process, causing internal wiring to break due to corrosion.
In some cases, the reliability was significantly reduced.

Accordingly, the present invention has been devised to effectively solve such a problem, and an object thereof is to provide an adhesive applying step and a ball terminal forming step performed in the final stage of a semiconductor assembling step. An object of the present invention is to provide a novel stress buffer layer and a TAB tape with ball terminals, which can omit a forming process and can improve the efficiency of a product assembling process and improve the yield.

[0010]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention relates to a TAB tape for connecting a semiconductor chip on a printed circuit board. A wiring pattern connected to the semiconductor chip is provided, and ball terminals connected to the printed board are provided on the wiring pattern. On the other hand, thermal stress between the semiconductor chip and the printed board is provided on the other surface of the polyimide tape. And a bonding agent for bonding the semiconductor chip on the stress buffer layer.

That is, the TAB tape of the present invention is provided with an adhesive and a ball terminal, which are conventionally applied on the stress buffer layer in the final step of assembling the semiconductor, and is integrally provided on the polyimide tape side in advance. .

Therefore, in the final step of assembling the semiconductor, the step of forming the adhesive and the ball terminals is not required, and the contamination and oxidation of the adhesive which have occurred in the final step of assembling the semiconductor due to the operation and effects described below. Inconveniences such as poor connection, void generation, repair work, selection and storage management of the adhesive, and internal disconnection due to corrosion can be effectively eliminated.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, a preferred embodiment of the present invention will be described with reference to the accompanying drawings.

FIG. 1 is a sectional view of an embodiment of a TAB tape with a stress buffer layer and ball terminals according to the present invention, and FIG. 2 is a partially enlarged view of FIG.

As shown in the figure, a wiring pattern 4 made of copper foil is formed on one surface (lower surface) of a long tape-shaped polyimide tape 2 with an adhesive 14 interposed therebetween. A land 6 having a circular opening in the solder resist 5 is formed, and a ball terminal 9 made of a solder ball is formed on the land 6.
On the other hand, a stress buffer layer 3 made of an elastomer is formed on the other surface (upper surface) of the polyimide tape 2 with an adhesive 7 interposed therebetween. An adhesive 12 for bonding to the third side is formed. The inner leads 10 extending from the wiring pattern 4 are respectively bonded to the semiconductor chip 1 via aluminum electrodes 11.

First, this polyimide tape 2 is usually
It is manufactured in units of 35 to 70 mm in width and 25 to 100 m in length, and has a thickness of about 50 to 70 μm. The copper foil for forming the wiring pattern 4 is about 18 to 25 μm. The adhesive 14 for bonding the wiring pattern 4 to the polyimide tape 2 side is 10 to 20.
An epoxy resin adhesive having a thickness of about μm is used.
A non-adhesive material or the like formed directly on the polyimide tape 2 by vapor deposition or sputtering of copper can also be used. These are CCL (Copper Clad Laminate)
It is called s), and has a feature of excellent flexibility because there is no adhesive layer.

The elastomer constituting the stress buffer layer 3 is made of a low elastic material having a thickness of about 50 to 150 μm.
Viscoelastic coefficient at 5-150 ° C is 100-1000M
A low elasticity elastomer of Pa is used. Specifically, it is a low elasticity epoxy resin containing a silicone resin or a rubber compound. The stress buffer layer 3 absorbs thermal stress between the glass epoxy resin wiring board (coefficient of thermal expansion: 10 to 20 ppm / ° C.) and the semiconductor chip 1. The stress buffer layer 3 is bonded to the polyimide tape 2 by an adhesive 7 having a thickness of about 5 to 10 μm.

The adhesive 12 for adhering the semiconductor chip 1 to the upper surface on the side of the stress buffer layer 3 is, in the case of a silicone resin-based elastomer, a mixture of an uncured silicone resin and a curing agent. The stress buffer layer 3 is formed by partial printing by a screen printing method.
When an epoxy resin-based elastomer containing rubber particles such as NBR is used as the stress buffer layer 3,
Also, an uncured epoxy resin monomer is blended together with a curing agent, and similarly formed by screen printing.

On the other hand, the ball terminals 9 are processed before forming the adhesive 12 on the stress buffer layer 3 because these adhesives are hardened in the melting and heating step of forming solder balls.
The ball terminals 9 are 0.3 mm from the polyimide tape 2.
In order to protrude by about 0.5 mm, in printing when forming the adhesive 12 on the stress buffer layer 3, it is necessary to form a concave portion for releasing the ball terminal 9 portion on a stage on which a printing tape is mounted.

After printing the solder paste, the ball terminal 9 is heated by a continuous reflow oven at 230 ° C. for about 10 seconds to melt the paste, or to form the already processed 0.3｀0.65 mmφ. The solder ball flux can be mounted on the printed land 6 and similarly formed by reflow heating and melting.

In this way, it is possible to form a TAB tape integrally including the stress buffer layer 3, the adhesive 12, and the ball terminals 9 with respect to the polyimide tape 2.
In the assembling step of the semiconductor chip 1, the temperature in the bonding step of connecting to the aluminum electrode 11 is 1
Since the temperature is 70 ° C., even when a eutectic solder ball having a melting point of 180 ° C. is used, the ball does not melt. In addition, since the curing temperature after sealing is 170 ° C., no melting occurs similarly.

[0022]

Next, specific examples of the present invention will be described.

(Embodiment 1) First, as shown in FIGS. 3 and 4, a polyimide tape 2 having a width of 35 mm, a thickness of 50 μm, and a length of 100 m was prepared.
An epoxy resin adhesive 14 having a thickness of 10 μm and a thickness of 10 μm is attached, and ILB
After opening the window 15 and the perforation hole 16, the width 26m
Rolled copper foil having a thickness of 18 μm and a thickness of 18 μm was bonded by a continuous laminator, and then a surface of the copper foil was coated with a photo solder resist by a roller coater, and then a wiring pattern 4 was formed by a photochemical etching method. The wiring pattern 4 includes lands 6 forming ball terminals 9, inner leads 10 connected to the aluminum electrodes 11 of the semiconductor chip 1, and copper foil wiring connecting these. After that, inner lead 1
A land 6 was formed by printing a photosensitive solder resist 5 having a thickness of 10 μm on the entire surface of the wiring pattern 4 except for 0, and then performing exposure and development.

The TAB tape manufactured in this way is 4
It has 8-pin inner leads 10 and 48 lands 6, and the wiring pitch of the inner leads 10 is 0.17 mm.
The diameter of the land 6 is 0.35 mm, and the pitch of the land arrangement is 0.75 mm.

The inner lead 10 and the land 6 were electroplated with gold to a thickness of 1.0 μm. Gold plating is performed on the aluminum electrode 11 of the semiconductor chip 1 and the Au-A
The connection is made by forming an alloy of l. It is also important for forming the ball terminals 9 to ensure the wettability of the solder.

Next, I on the other side of the polyimide tape 2
Inside the LB window 15, a 150 μm-thick silicon elastomer tape punched out by a die to the inside dimensions of the ILB window 15 is similarly adhered with the silicon adhesive 7 to form the stress buffer layer 3, and then this bonding is performed. After curing the agent 7, 37 mass% P is applied to the land 6 side.
A eutectic solder paste having a composition of b-Sn was printed using a metal mask, and then heated at 230 ° C. for 10 seconds to form a ball terminal 9. Thereafter, the ball terminals 9 were washed for 10 minutes at 60 ° C. in an aqueous detergent containing a surfactant. In addition, this washing | cleaning was performed by reel-to-reel system, unwinding a polyimide tape.

Finally, a silicone adhesive was printed on the stress buffer layer 3 to a thickness of 5 μm to produce a TAB tape having a stress buffer device with an adhesive 12 and ball terminals 9.
In addition, these steps were performed by a continuous winding system until the final adhesive application.

When the semiconductor chip 1 is mounted and adhered to the semiconductor assembly maker by using the stress buffer layer and the TAB tape with ball terminals, the semiconductor chip 1 is adhered under pressure at 160 ° C. for 2 seconds and then heated at 170 ° C. For 20 minutes.

(Example 2) In Example 1, as shown in FIG. 5, a hole was directly formed in the polyimide tape 2 without using a solder resist for forming a ball terminal, and a ball 17 was formed.
Was formed. In this case, a mold is required to form a hole in the mold, which increases the initial cost.However, since there is no photo process using a photosensitive solder resist, the tape manufacturing cost can be significantly reduced. .

Example 3 In Example 1, an elastic body made of an epoxy-based elastomer in which rubber particles of NBR (neoprene, butadiene, rubber) were blended was used for the stress buffer layer 3.

The silicon elastomer film in Example 1 has a viscoelastic coefficient at -50 to 150 ° C. of 100 M
On the other hand, the rubber particle-containing epoxy resin elastic body is 1000 MPa at −55 ° C. and 5 MPa at 150 ° C.
00 has a viscoelastic coefficient of MPa. Therefore, the effect of thermal stress buffering is small to the extent that the viscoelastic coefficient is high, but since it is about 1/3 of the value of a general epoxy resin, sufficient reliability can be exhibited in a temperature cycle environment. .

The adhesive applied on the stress buffer layer 3 was the same as that used in Example 1. Because this adhesive does not cure at room temperature, it does not cure during storage at room temperature for 6 months,
The semiconductor assembly maker can use the semiconductor chip even after long-term storage without any trouble in bonding the semiconductor chip.

When the semiconductor chip 1 is mounted and bonded using the stress buffer layer and the TAB tape with ball terminals in a semiconductor
After heating at 0 ° C for 2 seconds and bonding under pressure,
This can be achieved by curing for minutes.

Example 4 In Example 1, copper balls were used as the ball terminals 9 instead of the eutectic solder balls. Eutectic solder paste was printed on the connection of the copper balls, and copper balls were mounted thereon and reflowed.

Example 5 In Example 1, the ball terminals 9 were formed by printing conductive paste. The conductive paste is an epoxy resin, and contains copper particles to provide conductivity.

The curing temperature of this paste is 170 ° C., and a ball can be formed at a lower temperature than a solder ball. In addition, it has the advantage that cleaning is not required because no flux is used.However, there is a problem that it is not possible to connect with solder when mounting the board. The method is suitable.

Example 6 In Example 3, a thermoplastic adhesive was used as the elastomer adhesive.

The adhesive has a Tg of 210 ° C. At this temperature, the adhesive is softened and the semiconductor chip 1 can be connected. This polyimide has a sufficient adhesive strength to an epoxy resin-based elastomer and a semiconductor silicon chip.

[0039]

In summary, according to the present invention, the following excellent effects can be exhibited.

1. Since there is no need to apply an adhesive for bonding the semiconductor chip in the semiconductor assembling step, contamination of the aluminum electrode terminals of the semiconductor chip due to elution of the volatile solvent or the like can be avoided, and poor connection with the inner lead can be prevented. Further, in the semiconductor assembly process, there is no need to select the optimum adhesive every time, so that the mounting efficiency of the semiconductor chip is improved, and troublesome storage management of the adhesive is not required.

2. In the semiconductor assembling process, there is no special process of printing coat, so it is not necessary to enhance and improve the existing inner lead bonding process equipment.
Manufacturing costs can be reduced.

3. Since the ball terminals are not formed in the final step of assembly, there is no need for a heating step for melting the solder, and there is no inconvenience such as generation of voids at the interface between the semiconductor chip 1 and the polyimide tape.

4. Since the ball terminals are not formed in the final assembly process, the efficiency of mounting the ball terminals is greatly improved.
That is, in the present invention, several pieces can be collectively formed at the tape stage by solder reflow printing or ball mounting, and several pieces can be simultaneously formed at the same time.
Since zero semiconductor chips (480 balls) are collectively formed, ball terminals can be formed with ten times the capacity.

5. Since the formation failure of the ball terminals is greatly reduced, enormous labor and time required for repair can be reduced. Further, even if a defect occurs, the defect is identified before the semiconductor assembly process. Therefore, when repair is difficult, it is possible to directly dispose of the defect.

6 Since the ball terminals are formed immediately after the formation of the lands, connection failure due to the formation of an oxide film on the surface of the lands and contamination can be avoided.

7. Since the cleaning of the ball terminals is performed at the tape manufacturing stage, it is possible to prevent corrosion and internal disconnection inside the package due to mixing of cleaning water.

8. According to the effects 1 to 7, the overall yield is improved, and the manufacturing process is not wasted, so that the manufacturing efficiency can be improved and the cost can be reduced, that is, the product price can be reduced.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an embodiment of a TAB tape according to the present invention.

FIG. 2 is a partially enlarged view showing a portion A in FIG.

FIG. 3 is a plan view showing one embodiment of a TAB tape of the present invention.

FIG. 4 is a sectional view taken along line XX in FIG. 3;

FIG. 5 is a sectional view showing another embodiment of the TAB tape according to the present invention.

FIG. 6 is a cross-sectional view showing one embodiment of a conventional TAB tape with a stress buffer layer.

FIG. 7 is a partially enlarged view showing a portion A in FIG. 6;

8 is a view taken in the direction of arrows XX in FIG. 7;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Semiconductor chip 2 Polyimide tape 3 Stress buffer layer 4 Wiring pattern 5 Solder resist 6 Land 7 Elastomer adhesive 8 Printed circuit board 9 Ball terminal 10 Inner lead 11 Aluminum electrode 12 Semiconductor chip adhesive 13 Sealant 14 Copper foil adhesion Agent 15 ILB window 16 Sprocket hole

────────────────────────────────────────────────── ─── Continuing from the front page (72) Inventor Yasuharu Kameyama 3550 Kida Yomachi, Tsuchiura City, Ibaraki Prefecture Within Hitachi Cable Systems, Ltd. (56) References JP-A 9-116041 (JP, A) JP-A 10-116858 (JP, A) JP-A 9-321169 (JP, A) JP 8-83818 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01L 21/60 H01L 23/12

Claims (4)

(57) [Claims] 1. A TAB tape for connecting a semiconductor chip to a printed circuit board, comprising a wiring pattern connected to the semiconductor chip via inner leads on one side of a polyimide tape, and With ball terminals connected to the printed circuit board,
On the other hand, the other surface of the polyimide tape includes a stress buffer layer for absorbing thermal stress between the semiconductor chip and the printed board, and an adhesive for bonding the semiconductor chip on the stress buffer layer. A TAB tape with a stress buffer layer and a ball terminal. 2. The low-elastic elastomer and adhesive according to claim 1, wherein the stress buffer layer and the adhesive have a viscoelastic coefficient of 100 to 1000 MPa at −55 to 150 ° C., respectively. A TAB tape with a stress buffer layer and ball terminals, characterized by comprising an agent. 3. The TAB tape with a stress buffer layer and a ball terminal according to claim 1, wherein the adhesive is:
A TAB tape with a stress buffer layer and ball terminals, comprising a thermoplastic polyimide resin or an uncured epoxy resin containing a curing agent. 4. The TAB tape with a stress buffer layer and a ball terminal according to claim 1, wherein the ball terminal is a eutectic solder ball of 37Pb-Sn formed by solder paste printing reflow, or A TAB tape with a stress buffer layer and ball terminals, comprising a solder ball formed by a mounting method, a metal ball connected by solder, or a conductive resin such as a conductive epoxy resin.