JP3449047B2 - Lead frame structure - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lead frame structure composed of a thin multi-pin lead frame used for semiconductor devices and the like, and more particularly to a semiconductor in a portion surrounded by inner leads on four sides of the lead frame. The present invention relates to a lead frame structure having no island for mounting an integrated circuit chip.

[0002]

2. Description of the Related Art An example of a method for manufacturing a lead frame is shown in FIG.
Will be briefly explained. First, a water-soluble negative photosensitive resin made of, for example, casein or polyvinyl alcohol and ammonium dichromate is applied to both surfaces of the metal plate 7 to be the lead frame to form a photosensitive resin layer. Next, two substantially the same pattern masks in which the pattern frame portion of the lead frame is used as the light transmitting portion and the portions other than the lead frame pattern portion are used as the light shielding portion are used. Another pattern mask is applied to the opposite position of the other surface of the metal plate 7, and ultraviolet light exposure is performed from both surfaces to photo-cure the photosensitive resin layer in the pattern pattern of the lead frame.

Then, development is performed to remove the photosensitive resin layer in the uncured portion, that is, the photosensitive resin layer other than the portion to be the pattern of the lead frame, and the remaining photosensitive resin layer is subjected to a film hardening treatment. Then, a burning process is performed to obtain an etching resistant layer 8 which exposes the metal plate 7 other than the portion to be the pattern of the lead frame, as shown in FIG. 6 (a). Next, as shown in FIG. 6B, the metal plate 7 is etched from both sides with an etchant, and the metal plate 7 other than the portions to be the pattern of the lead frame is removed by etching to form the pattern of the lead frame. Except for the parts that are to be formed, the parts that will be the pattern of the lead frame are left.

Next, as shown in FIG. 6 (c), after removing the etching resistant layer 8 from the metal plate 7, the metal plate 7 is cut into an appropriate size if necessary. In addition, the appropriate size here means to make it a single-wafer state of a size that is easy to carry, and to cut the lead frame body at the boundary area of the multi-faced lead frame so as not to scratch it. is there. Next, a partial noble metal plating process is performed on the tip regions of the inner leads by a known method. Then, unnecessary portions of the metal plate 7 are punched out and removed to finally obtain a lead frame.

At present, the lead frame has a thin plate thickness and tends to have a large number of pins. For example, in some lead frames for ceramic packages, the package size is large, the number of pins is from 200 pins to 300 pins or more, and the plate thickness is very thin, about 100 μm to 150 μm.

An example of FIG. 3 is shown in the process of manufacturing the lead frame 4 which is thin and has a large number of pins, and there is no island for mounting a semiconductor integrated circuit chip in a portion surrounded by inner leads on four sides. So the frame
The lead frame 4 formed in 10 is provided with a portion called a connecting flap 6 and a dummy pattern 5,
These are collectively referred to as the lead frame structure 2. The frame 10 in FIG. 3 is formed on the outer periphery of the lead frame 4 for holding the lead frame 4, and there may be a case where a plurality of lead frames 4 are attached inside the frame 10. Here, the connecting flaps 6 connect the front end groups on each side of the inner leads 3 on the four sides. That is, the inner lead 3 has a small width and a small thickness, and the inner lead 3 is not affected by an external force applied to the lead frame portion during manufacturing.
Since it is liable to be deformed, in order to prevent this, the connecting flaps 6 are used to connect the front end groups on each side of the inner leads 3 to provide structural reinforcement.

Next, for example, a ring-shaped dummy pattern 5 provided in the central portion of the lead frame 4 shown in FIG. 3 is connected to each connecting flap 6. Partial noble metal plating on the tip end region of the inner lead 3 is performed by sandwiching the lead frame structure 2 between the back sheet 11 and the mold 12 having a predetermined opening, as shown in FIG.
It is performed by spraying the plating liquid 14 on the lead frame structure 2 portion exposed from the mold 12, that is, on the tip end region of the inner lead 3. At that time, the connecting flap 6
The purpose of this is to prevent the deformation of the tip portion of the inner lead 3 by the pressure of the plating liquid 14 sprayed on the tip portion area of the inner lead 3 by locking the dummy pattern 5 connected with the presser bar 13 or the like. By the way, the part of the dummy pattern 5 that comes into contact with the pressing rod 13 is the pressing rod 13
Since this masks the plating solution 14, it is the part that is not plated. Finally, from the lead frame structure 2 to the frame 10, the connecting flaps 6 and the dummy patterns 5 in FIG.
Unnecessary parts such as are cut and removed to obtain the lead frame 4. Further, the connecting flap 6 and the dummy pattern 5 in the drawing show a large width for the sake of explanation, but in reality, the width is as thin as about 0.5 mm.

When manufacturing a semiconductor device using the lead frame 4 obtained in the above-described manufacturing process, a tip portion of each inner lead 3 plated with a partial noble metal and a semiconductor integrated circuit chip corresponding to each inner lead are formed. The connection pads are electrically connected by, for example, bonding with a thin wire. Therefore, it is necessary to inspect after the partial noble metal plating process whether the partial noble metal plating applied to the tip end regions of the inner leads 3 is as desired, for example, has a desired plating thickness. That is, if the plating process such as thin plating is insufficient, connection failure or the like occurs during the above-mentioned wire bonding.

Usually, this inspection is carried out by measuring, for example, the glossiness, that is, the optical reflection density of the portion where the partial noble metal plating is applied.

The usual measurement of optical reflection density is carried out using an optical reflection densitometer. The measurement method using an optical reflection densitometer is to irradiate a spot with a diameter of about 2 to 3 mm to the measurement point and calculate the optical reflection density at the measurement point based on the amount of light reflected from the light irradiation point.

However, as described above, the lead frame has multiple pins, and the width of the inner lead is, for example,
It is extremely thin, about 0.1 mm. Therefore, as shown in FIG. 4, even if the spot light irradiation is performed on the tip end region of the inner lead 3 on which the partial noble metal plating 9 shown by the diagonal lines is applied, a plurality of inner leads 3 within the spot light irradiation region 15 are formed. However, it can be said that, for example, it enters into the shape of comb teeth. A recess is formed between the inner leads 3, and the irradiation light is not reflected or is a scattered light in this recess. For this reason,
It can be said that the reflected light due to the spot light irradiation on the inner lead 3 portion is an incomplete reflected light, and it is difficult to measure the optical reflection density of the partial noble metal plating portion on the inner lead 3. In particular, in the lead frame 4 for ceramics package shown in FIG. 3, there is no island for mounting the semiconductor integrated circuit chip in the central region, and the portion to which the partial precious metal plating is applied is the inner lead 3 described above.
It can be said that only the narrow portion of the connecting flap 6 and the dummy pattern 5 is formed. Therefore, even if spot light irradiation is performed to measure the optical reflection density, as shown in the example of FIG. 4, for example, the spot light irradiation area 15 having a diameter of about 2 to 3 mm is used.
Since a plurality of patterns are included inside, and there is no portion having an area enough to receive all the spot light with one pattern, it is difficult to measure the optical reflection density of the partially noble metal plated portion.

[0012]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances, and uses an optical reflection densitometer to mount a multi-pin and a semiconductor integrated circuit chip plated with a partial noble metal. It is an object of the present invention to provide a lead frame structure capable of easily measuring the glossiness of a lead frame having no island to be placed.

[0013]

That is, according to the present invention, in a lead frame structure in which there is no island for mounting a semiconductor integrated circuit chip in a portion surrounded by inner leads on four sides of the lead frame, a portion to the inner lead is provided. To solve the above problems by providing a lead frame structure characterized in that a measurement pattern having a predetermined size, which is plated at the same time as precious metal plating, is provided in the central region of the lead frame. Is.

The present invention will be described below with reference to the drawings. In the lead frame structure 2 according to the present invention, for example, as shown in FIG. 1, the lead frame 4 is provided with the connecting flap 6 and the dummy pattern 5 as in the conventional case. A pattern for measurement (hereinafter, simply referred to as a measurement pattern 1) is provided, which is a feature of the present invention.

As described above, the measurement of the glossiness of the partial noble metal plating applied to the inner lead 3 part is carried out in the measurement pattern 1 part. Therefore, the measurement pattern 1 is provided at a position where the measurement pattern 1 can be simultaneously plated with the partial noble metal when the inner lead 3 is partially plated with the noble metal. For example,
During partial precious metal plating, the dummy pattern 5 has a pressing rod 13
In the measurement pattern 1, at least a region corresponding to the diameter of the spot light emitted from the optical reflection densitometer is exposed from the pressing rod 13 so as to come into contact with the plating solution, or It is provided at a position apart from the presser bar 13.

Normally, the lead frame structure 2 has the structure shown in FIG.
As shown in the example, the partial noble metal plating 9 is applied to the shaded area surrounded by the two broken lines. By providing the measurement pattern 1 at the above-mentioned position, the partial noble metal plating is also applied to the measurement pattern 1. 9 will be given. The broken line A in the figure indicates the region of the pressing rod 13. Next, the glossiness is measured using an optical reflection densitometer on the measurement pattern 1 part where the noble metal plating 9 is applied similarly to the inner lead 3 part. By the way, dummy pattern 5
An area without a diagonal line is a portion where the plating liquid is masked by the pressing rod 13.

Here, it can be said that the size of the measurement pattern 1 is at least as large as the diameter of the light irradiation region 15 shown in the example of FIG. 4, but the deviation of the light irradiation portion at the time of density measurement. In consideration of the above, it can be said that it is desirable to have a region larger than the diameter of the light irradiation region 15 to be irradiated. For example, when the diameter of the light irradiation area 15 is about 2 to 3 mm, the diameter of the measurement pattern 1 is about 5 mm.

As described above, the size and the position of the measurement pattern 1 of the present invention are determined by the diameter of the light irradiation area 15 peculiar to the optical reflection densitometer used, the thickness of the pressing rod, and the lead. Because it depends on the manufacturing specifications of the frame,
It can be said that it is desirable to set it appropriately.

The lead frame structure 2 of the present invention
Is not limited to the shape described above. For example,
Although the shape of the measurement pattern 1 is circular in FIG. 1, it may be square.

Further, in FIG. 1, the measurement pattern 1
, Are connected to the dummy pattern 5 at two places, it can be said that the connection may be made to the connecting flap 6. However, when the lead frame structure 2 is conveyed after the etching process, the measurement pattern 1 is subject to vibration and external force.
It can be said that it is desirable to connect the measurement pattern 1 to at least one of the dummy pattern 5 and the connecting flap 6 at a plurality of positions so that the measurement pattern 1 does not fall off or deform.

As described in the above section (prior art), the lead frame structure 2 of FIG.
The connecting flap 6 and the dummy pattern 5 are cut and removed, but at the same time, the measurement pattern 1 is also cut and removed, and finally a lead frame similar to the conventional one is obtained.

[0022]

In the lead frame structure according to the present invention, the inner lead is partially plated with the noble metal, and at the same time, at least the measurement pattern 1 having the size of the spot light irradiation area irradiated by the optical reflection densitometer is formed. ,
Plating is performed similarly to the inner lead. Then, the optical reflection densitometer is used to measure the reflection density of the measurement pattern 1 part, whereby the quality of the plating process performed on the inner leads can be determined.

[0023]

EXAMPLES Examples of the present invention are shown below. <Example> Using a metal plate having a plate thickness of 125 μm,
The lead frame structure 2 shown in FIG. 1 is manufactured in accordance with the manufacturing process described in (Prior Art), and after performing partial silver plating on the tip end region of the inner lead 3, punching using a die is performed. We obtained a lead frame for a 208-pin ceramics package. The width of the inner leads 3 of this lead frame and the distance between the inner leads were each 0.1 mm.

At this time, the connecting flap 6 and the dummy pattern 5 are formed on the lead frame structure 2 as in the conventional case. However, according to the present invention, as shown in FIG. For this purpose, a circular measuring pattern 1 was provided, and the dummy pattern 5 was connected at two locations. In addition, when the inner lead 3 is partially silver plated,
The measurement pattern 1 was provided at a site where partial silver plating was performed on the entire measurement pattern 1 without being disturbed by 13.

Then, the glossiness of the plated portion after the partial silver plating treatment was measured by using a digital optical densitometer (trade name "GAM digital densitometer MODEL 144" manufactured by Graphic Arts Marketing Inc., USA). Was measured. The spot light diameter of the above optical densitometer was 1.58 mm.

Therefore, the measurement pattern 1 according to the present invention
The size of is set to about 4 mm in diameter considering the deviation of the light irradiation area.

Then, after the partial silver plating treatment, the reflection density was measured with one part of the measurement pattern using the above-mentioned digital optical densitometer.

[0028]

In the lead frame structure according to the present invention, at least the size of the spot light irradiation area of the optical reflection densitometer used is measured at the position where the inner lead is subjected to plating during partial noble metal plating. There is a pattern for use. That is, the inner lead is partially plated with the noble metal, and at the same time, the measurement pattern is plated in the same manner as the inner lead. This makes it possible to easily judge the quality of the plating process performed on the inner leads by measuring the reflection density of the plated measurement pattern portion using a conventional optical reflection densitometer, and It can be said that it is practically excellent in obtaining a good lead frame.

[0029]

[Brief description of drawings]

FIG. 1 is an explanatory plan view showing an embodiment of a lead frame structure of the present invention.

FIG. 2 is an explanatory plan view showing an example of partial noble metal plating on the lead frame structure of the present invention.

FIG. 3 is an explanatory plan view showing an example of a conventional lead frame structure.

FIG. 4 is a plan view showing an example of spot light irradiation on an inner lead portion.

FIG. 5 is a cross-sectional view showing an example of a method of partially plating a noble metal on a lead frame.

6A to 6C are explanatory views showing an example of a conventional lead frame manufacturing method in the order of steps.

[Explanation of symbols]

1 Measurement pattern 2 Lead frame structure 3 inner lead 4 lead frame 5 Dummy pattern 6 connecting flaps 7 metal plate 8 Etching resistant layer 9 plating 10 frames 11 back sheet 12 formwork 13 Presser bar 14 Plating liquid 15 Light irradiation area

─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP 59-139659 (JP, A) JP 7-66351 (JP, A) JP 8-37267 (JP, A) JP 61- 252653 (JP, A) JP-A-8-162601 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H01L 23/50

Claims (2)

(57) [Claims] 1. In a lead frame structure having no island for mounting a semiconductor integrated circuit chip in a region surrounded by inner leads on four sides of a lead frame, the inner leads are plated at the same time when a partial noble metal is plated. A measurement pattern having a size,
A lead frame structure provided in a central area of the lead frame. 2. A lead frame structure in which there is no island for mounting a semiconductor integrated circuit chip in a region surrounded by inner leads on four sides of a lead frame, and a connecting flap for connecting a tip group on each side of the inner leads on four sides. Alternatively, when the inner lead is partially plated with a noble metal, it is connected to at least one of the dummy patterns provided in the center of the lead frame for the purpose of preventing the inner lead from being deformed. A lead frame structure, wherein a measuring pattern having a size is provided in a central region of the lead frame.