JP3341581B2 - Lead frame for semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress defective bonding by setting the leads for starting and ending the coating of adhesive varnish wider than other inner leads. SOLUTION: The lead frame for semiconductor device has inner leads 20-1 ,..., 20-5 coated with an adhesive varnish in the region for mounting a semiconductor chip. The width W1 of the first and end leads 20-1 , 20-5 is set at least 1.3 times wider than the width W2 of other inner leads 20-2 ,..., 20-4 in order to suppress fluctuation of the coating.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a method for manufacturing a lead frame for a semiconductor device used for a semiconductor device such as LOC and COL.

[0002]

2. Description of the Related Art For example, DRAM (Dynamic Random Acceses)
Conventionally, a package structure in which a semiconductor chip is mounted on a lead frame up to 1 Mbit and terminal pads of the semiconductor chip are connected to inner leads of the lead frame by bonding wires is used. But,
With the recent increase in capacity, for example, C
OL (Chip On Lead) structure, LOC for 16Mbit
(Lead On Chip) package structure.

FIG. 2 is a front sectional view showing an example of a semiconductor device having a LOC package structure. The lead frame 1 used for the LOC package includes an inner lead 2, an outer lead 3 connected to the inner lead 2, and a resin tape 4 attached to a semiconductor chip mounting area 2 a of the inner lead 2.
It is comprised with. The inner lead 2 and the outer lead 3 are manufactured by etching or pressing. For example, a polyimide film can be used for the resin tape 4, and an adhesive made of a thermoplastic resin or a thermosetting resin is applied to both surfaces thereof. After punching this tape into a predetermined pattern using a punching die, a predetermined position of the lead frame (inner lead portion)
Affixed to

Here, the assembly of a semiconductor device using the lead frame 1 will be described. First, after positioning the semiconductor chip 5 with respect to the lead frame 1, the semiconductor chip 5 is attached to the resin tape 4. Then, a predetermined portion of the inner lead 2 is connected to the terminal pad 6 of the semiconductor chip 5 by a bonding wire 7 using a bonding tool (not shown). Thereafter, the semiconductor device 9 is completed by molding with a mold resin 8 into a shape surrounding the inner leads 2 and the semiconductor chip 5.

[0005] However, according to the lead frame having the configuration shown in FIG. 2 using a tape, a dedicated die and a bonding device are required for each lead frame type. Also, since the tape is expensive, the lead frame becomes expensive. On the other hand, FIG.
In place of the resin tape 4, there is a lead frame formed by applying an adhesive varnish using a thermoplastic resin or a thermosetting resin to form a coating film. A dispenser or screen printing is used for applying the adhesive varnish. Since a solvent is mixed in the adhesive varnish, the solvent is evaporated over a predetermined temperature and time after application. The lead frame to which the adhesive varnish is applied has the following features as compared with the tape system. (A) The required minimum amount of adhesive varnish can be applied only to necessary portions such as the lead portion, and a base material such as a polyimide film is not required. it can. (B) Since no base material such as a polyimide film is used, the amount of the polymer material contained in the package can be reduced. This leads to a reduction in the amount of moisture absorption, and can reduce the occurrence of package cracks due to solder reflow.

Next, a coating apparatus 10 for coating an adhesive varnish and a coating method using the same will be described.
As shown in FIG. 2, an adhesive varnish using a thermoplastic resin or a thermosetting resin is formed of inner leads 11 _{-1 to} 11 _-8 arranged at regular intervals using a coating device 10 (here, the description will be omitted). (For convenience, the number is eight, but the number is arbitrary.) The upper surface of each of them is successively applied in a semi-cylindrical shape to form a coating film 12 (step 101).

The coating device 10 includes a needle 13 and a barrel 1
4 and a controller 15. Vinyl between barrel 14 and controller 15,
They are connected by a flexible air pipe 16 made of a material such as rubber. The needle 13 is made of, for example, stainless steel and has an inner diameter of about 0.34 mm and an outer diameter of 0.64 mm.
φ, has a pipe-like shape made about 13mm in length,
A liquid adhesive varnish is discharged from the tip. The barrel 14 provided integrally with the needle 13 is made of a material such as polypropylene. Its volume is 30
cc, and incorporates an adhesive varnish 14a (for example, a polyetheramideimide-based thermoplastic resin).
Air is supplied to the needle 13 by air pressure supplied from an air pump (not shown) in the controller 15. The controller 15 includes a circuit and a mechanism for controlling the discharge pressure and the discharge time of the adhesive varnish so that the coating film 12 has an appropriate amount. In order to apply the coating film 12 properly, the inner leads 11 _-1 to 1 _{-1 of the} needle 13 are further required.
It is necessary to optimize the conditions such as the interval from _1-8 and the needle moving speed. If such conditions are prepared, the adhesive varnish can be applied without spilling between the adjacent inner leads 11 _{-1 to} 11 _-8 .

After applying the coating film 12 to each of the inner leads 11 _{-1 to} 11 _-8 using such a coating device 10,
The solvent contained in the coating film 12 is dried. This drying process is performed by setting on a hot plate heated to a predetermined temperature for several minutes.

[0009]

However, according to the conventional lead frame coated with the adhesive varnish, when the coating is started, gravity is applied to the tip of the needle 13, and
Due to the surface tension of the adhesive varnish, etc., FIG.
As shown in FIG. 7, a varnish dripping 17 occurs. When the discharge of the adhesive varnish is started while the dripping 17 is generated,
The lead to be applied first (for example, inner lead 1
1 _-1 ), the amount of [set discharge amount + liquid dripping 17] is applied, and as shown in FIG. 5A, the film thickness is smaller than that of the lead coating film 12 applied after the second. Large coating film 12
a is formed, the film thickness between the leads varies, and a bonding failure easily occurs during bonding.

When the amount of application is large, a liquid spill 18 flowing to both sides occurs as shown in FIG. 5B. Alternatively, as shown in FIG. 5C, a bridge 19 is formed between the leads, and a connected state occurs. When the state as shown in FIGS. 5B and 5C occurs and the adhesive varnish goes around the back surface of the lead, it causes a bonding failure. The above problem occurs not only in the lead for starting the coating but also in the lead for finishing the coating. That is, as a result of the varnish being discharged more than a predetermined amount due to the inertia effect, the same problem as the coating start lead occurs.

SUMMARY OF THE INVENTION An object of the present invention is to provide a lead frame for a semiconductor device in which a coating start lead and a coating end lead of an adhesive varnish can be made almost the same thickness as other leads.

[0012]

In order to achieve the above object, the present invention provides a lead frame for a semiconductor device in which an adhesive varnish is applied by a dispenser to an area where a semiconductor chip of an inner lead is to be mounted. Among them, the width of the lead for applying the adhesive varnish and the lead for applying the adhesive varnish are made wider than the width of the other leads.

[0013] According to this configuration, since the lead width of the coating start lead and the coating end lead in which the application amount of the adhesive varnish is larger than that of the other leads is wide, the applied adhesive varnish diffuses in the width direction. Therefore, if the lead widths of the coating start lead and the coating end lead are optimally set, the film thickness can be made substantially the same as the other leads, and the variation in the film thickness between the leads can be made extremely small. As a result, bonding failure during bonding can be made less likely.

It is preferable that the coating start lead and the coating end lead are at least 1.3 times the width of the other leads. According to this configuration, even when the amount of the adhesive varnish applied is large, the lead surface with the increased amount of the excess varnish bears, so that dripping, bridges, excessive film thickness, and the like do not occur.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described.
This will be described with reference to the drawings. FIG. 1 shows a semiconductor device according to the present invention.
FIG. 2 is a perspective view showing a configuration of a main part of a lead frame for use.
In the present invention, as shown in FIG.
The frame has five inner leads 20 on one side._-1~ 20_-Five
In case of having an inner
-Reed 20_-1And inner end 20 of coating_-FiveOnly
Other inner leads 20_-3~ 20_-FourMake it wider than
I have. That is, the coating start inner lead 20_-1And application
End inner lead 20_-FiveWidth W₁Is the other inner
Code 20 _-3~ 20_-FourWidth W_TwoTo the ratio, W₁: W_TwoTo
The ratio is set to 1.3: 1 or more. This value
Then, an appropriate coating thickness can be formed. Note that
The lead thickness t is the same for all leads.

As described above, the coating start inner lead 20
_{By -1} and a width W ₁ of the coating end inner leads 20 _-5 and wider than the other inner leads 20 _-3 to 20 _-4, coating start inner leads 20 _-1 and coating end inner leads 20 _-5 Even if a large amount of adhesive varnish is applied to
Since the adhesive varnish after application spreads in the lead width direction,
The coating film 12a becomes substantially the same as the coating film 12 applied to the other leads, and the film thickness is made uniform. For this reason, the conventional bonding failure is unlikely to occur.

[0017]

Next, an embodiment of the present invention will be described. Here, a dispenser method was used as a means for applying the adhesive varnish. A polyether amide imide-based thermoplastic resin was used for the adhesive varnish. The adhesive varnish has a solid content of about 100 Pa · s at 25 ° C.
wt%. The adhesive varnish was filled into a barrel 14 having a volume of about 30 cc and sealed.

The lead frame has a thickness t of 0.15 mm.
To etch plate material made of Fe-42% Ni alloy
And the “sample 1” according to the prior art and the “sample 1” according to the present invention.
2 ". Note that all lead intervals are 0.3mm
did. "Sample 1" has an inner lead as shown in FIG.
11_-1~ 11_-FiveAll conventional technologies with the same width (0.3mm)
It was made by art. "Sample 2" is shown in FIG.
Was manufactured according to the present invention as shown in
First Inner Lead 20 _-1And inner end 20 of coating
_-FiveWidth W₁To 0.5 mm and the other inner leads 20
_-3~ 20_-FourWith a width of 0.3 mm
You. “Sample 1” and “Sample 2” are the same material.
(Fe-42% Ni alloy) and the manufacturing process is the same.
One. 1 and 6, for convenience of explanation,
Although the number of cables is set to 5, actually one lead frame
There are about 320 in them.

An adhesive varnish was applied to the inner lead portions of the two types of lead frames using the application device 10 shown in FIG. In this application, the needle 13 was continuously discharged and moved from one side of the inner leads 20 _{-1 to} 20 _-5 of the lead frame toward the other (without stopping between the leads). The application conditions were a discharge pressure of 3.5 kg / cm ² , a needle moving speed of 10 mm / s, and a distance between the lead frame and the tip of the needle of 0.15 mm. This condition is when the target value of the thickness of the coating film 12 after drying the solvent is set to about 30 μm. Therefore, if the target value of the coating film thickness changes, the coating conditions also need to be changed. Solvent drying was performed using three hot plates. The heating temperature of each hot plate was set at 100 ° C., 200 ° C., and 300 ° C.
100 ° C. → 200 ° C. after lead 2 is formed
→ Each of them was conveyed for 5 minutes in the order of 300 ° C.

As described above, the adhesive varnish was applied to 100 lead frames, and the thickness of each lead was measured. The thickness of the coating film is measured using a commercially available focus microscope (for example, one having an accuracy capable of detecting a difference of up to 0.1 μm), and a lead (F) near the coating film surface and the coating film 12 is used.
e-42% Ni alloy)
Table 1 (for "Sample 1") and Table 2 (for "Sample 2")
) Were obtained.

[0021]

[Table 1]

In the conventional lead frame shown in Table 1, the minimum value is 9.9 μm (38.9 μm−29.0 μm).
m = 9.9 μm), and 12.6 μm (4
(3.1 μm−30.5 μm = 12.6 μm). The maximum value is 23.9 μm (55.6 μm−
31.7 μm = 23.9 μm). As described above, a large thickness variation is observed in the conventional lead frame.

[0023]

[Table 2]

On the other hand, as shown in Table 2, the lead frame according to the present invention has a minimum value of 1.2 μm (30.1 μm-
Height difference of 28.9 μm = 1.2 μm), average 0.8
μm (31.3 μm−30.5 μm = 0.8 μm). The maximum value is 1.3 μm (32.9 μm).
m-31.6 μm = 1.3 μm). in this way,
The lead frame of the present invention was able to make the difference in height (difference in film thickness between leads) extremely small as compared with the conventional lead frame. As a result, it is possible to prevent occurrence of bonding failure in the wire bonding step.

[0025]

As described above, according to the present invention, the inner
Dispenser for lead semiconductor chip mounting area
Lead frame for semiconductor device coated with adhesive varnish
In the system, the width of the adhesive varnish application start lead and the application ending lead among the inner leads is made wider than the width of the other leads, so that the excess of the adhesive varnish diffuses in the width direction. Therefore, the variation in the film thickness between the leads can be made extremely small, and the bonding failure at the time of bonding can be made hard to occur.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a detailed configuration of an inner lead portion of a lead frame for a semiconductor device of the present invention.

FIG. 2 is a schematic configuration diagram of a coating device used in a varnish coating step in the lead frame manufacturing method of the present invention.

FIG. 3 is a front sectional view showing an example of a semiconductor device having a LOC package structure.

FIG. 4 is a front view of a needle tip showing a state in which varnish dripping has occurred in a conventional lead frame.

FIGS. 5A and 5B are front views showing examples of coating defects in a conventional lead frame, wherein FIG. 5A shows a state in which a coating film has a difference in height due to a large coating amount of a specific lead, and FIG. A state in which liquid spills on the side of the lead is shown, and FIG. 3C shows a state in which a bridge is formed between the leads.

FIG. 6 is an enlarged perspective view showing details of an inner lead portion of a conventional lead frame.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Lead frame 10 Coating device 11, 11 _{-1 to} 11 _-5 , 20 _{-3 to} 20 _-4 Inner lead 12 Coating 13 Needle 20 _-1 Coating start inner lead 20 _-5 Coating end inner lead

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-5-218111 (JP, A) JP-A-62-296541 (JP, A) JP-A-6-291156 (JP, A) International publication 95/29506 (WO, A1) (58) Field surveyed (Int. Cl. ⁷ , DB name) H01L 23/50 H01L 21/52

Claims (2)

(57) [Claims] 1. A lead frame for a semiconductor device in which an adhesive varnish is applied to a region where a semiconductor chip of an inner lead is to be mounted by a dispenser , wherein a width of a lead for starting application of the adhesive varnish and a lead for ending application of the adhesive varnish are included. A lead frame for a semiconductor device, which is wider than other leads. 2. The lead frame for a semiconductor device according to claim 1, wherein the application start lead and the application end lead are at least 1.3 times as wide as the other leads.