JPH08204093A - Bending die of lead frame - Google Patents

Abstract

PURPOSE: To enhance the abrasion resistance and work a shape of a working part with high precision by a method wherein an average thickness of a metal Co phase being a coupling phase is made less than a specific value. CONSTITUTION: WC of 1μm or less is manufactured by being directly carbonized from a specific mixture of particles W and carbon, and this is mixed with a specific amount of Co and molded at 0.5 to 2T/cm<2> and sintered for one hour at about 1300 to 1450 deg.C in a vacuum. Further, this is processed with a hot hydrostatic pressure press (HIP) at 1200 to 1350 deg.C at <1000 atmosphere to manufacture a superhard alloy material having particles and high viscosity. The superhard alloy is mainly composed of WC having an average crystalline particle size 1μm or less and TiC, and if an average thickness of a metal Co phase being a coupling phase is 0.15μm or less, a plating adhering amount becomes half or less, preferably. Further, if a surface roughness enhances, the plating adhering amount reduces naturally, and a 10-point average maximum height roughness is 1μm or less based on JIS B0601.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lead metal-bending metal mold used for shaping a lead frame having a semiconductor chip mounted therein, that is, for bending a lead in an assembly process of a semiconductor device.

[0002]

2. Description of the Related Art In the process of assembling a semiconductor device,
Fix the semiconductor chip to the lead frame or package,
The electrodes of the chip and the leads of the lead frame are connected by wires and sealed with resin or the like, and then the leads are bent. The material of this conventional shaping die is hardened steel or cemented carbide, and the processed portion is formed by performing surface finishing by polishing.

However, in the molds using these materials, there is a big problem that the lead bending accuracy is poor due to the solder plating used for fixing the chip on the printed wiring board to the surface of the processed part of the mold. Has become.
If you continue to shape the lead while solder is still attached to the mold surface, lead deformation such as foot bending will occur, and when soldering on the printed wiring board in the subsequent process, poor soldering, poor contact, short circuit with left and right pins will occur. The problem occurs that the completed printed wiring board does not operate normally. Therefore, in order to remove the adhered plating, the mold had to be regularly removed from the apparatus and lapped to be removed.

Therefore, in Japanese Unexamined Patent Publication No. 4-280500, a brush cleaning or air blow cleaning mechanism which is interlocked with a moving mechanism of the product at the time of bending the outer lead of the lead frame is attached to force the solder attached to the mold. The method to exclude is presented. However, if the solder plating strongly adhered to the mold is removed, problems like mold deformation and mold life will occur as in the past, and space problems will occur when mounting to conventional equipment. .

In order to solve such a problem, Japanese Unexamined Patent Publication (Kokai) No. 2-28964 proposes a method in which a groove is formed in a portion of the bending punch surface or the bending die surface where the semiconductor leads come into contact with each other to prevent the adhesion of solder residue. . However, it is expensive to mold the groove on the entire surface of the portion where the solder residue is adhered, and the processing after the deposition of the solder residue in the groove is difficult, which causes a problem in maintenance.

Japanese Patent Laid-Open No. 2-134856 discloses that the surface of a lead frame contact portion of a cutting mold has excellent wear resistance, non-adhesiveness, and sliding characteristics of 5 to 10 μm in order to prevent solder from adhering to the mold. The method of applying the amorphous chrome plating film is disclosed. Also, JP-A-63-203222
No. 203223, steel for metal working, Si ₃ N ₄ , Al by plasma CVD method etc.
Means for coating ceramics such as ₂ O ₃ , diamond and SiC are disclosed. However, these films have problems such as poor adhesion to the substrate and poor surface roughness immediately after film formation. In order to form a ceramic film with high adhesion, it is necessary to form a film at a high temperature, and it is necessary to consider the thermal expansion between the ceramic to be formed and the base material, which poses a problem of limiting the base material. It was

[0007]

DISCLOSURE OF THE INVENTION The present invention can improve wear resistance and achieve high precision machining of the shape of a machined portion, and can suppress chemical reactivity with a lead frame material or solder. The number of steps to remove deposits and adhesions on the mold surface can be reduced, and the life can be significantly improved and improved compared to conventional molds, and even if solder adheres to the mold due to long-term use, simple work is possible. It is an object of the present invention to provide a die for bending a lead frame capable of removing it.

[0008]

As a means for solving the above-mentioned problems, in the lead frame bending die provided by the present invention, at least the die processed portion is made of a cemented carbide material. And is therefore characterized by
The entire mold does not have to be made of a cemented carbide material. However, the cemented carbide material is mainly composed of a hard carbide such as WC having an average crystal grain size of 1 μm or less, and an average thickness of a metallic Co phase as a binder phase is 0.15 μm or less. .

Cemented carbide has wear resistance, high Young's modulus, and high hardness characteristics, so that high precision machining is possible. Therefore, it is more advantageous than the conventional steel-based material in terms of maintaining the shape of the bent tip end portion of the die, and this greatly affects the processing characteristics of the lead frame. Furthermore, since the coefficient of thermal expansion is extremely smaller than that of steel-based materials, the deformation of the mold due to heat generated during continuous processing of the lead frame is small, and it is expected that the accuracy of mold processing can be maintained.

Further, the cemented carbide of the mold suppresses the reactivity with solder and lead frame scraps, which makes it difficult for the solder and the scraps to adhere or adhere during bending of the lead frame. In addition, the cemented carbide has excellent wear resistance, and therefore, the shape of the cemented carbide is hardly deformed when the deposit is removed. This cemented carbide is mainly composed of WC or W having an average crystal grain size of 1 μm or less.
If the average thickness of the metallic Co phase, which is a binder phase, is 0.15 μm or less, it is composed of hard carbides such as carbides and nitrides of Group IVa, Va, and VIa of the periodic table such as C and TiC.
Because the WC crystal grains are finely dispersed on the surface of the cemented carbide, Co
The phase becomes thin. As a result, the coefficient of friction between the Co phase and the solder or the deposit becomes small, the diffusion of atoms due to the friction between the Co and the solder or the deposit can be suppressed, and the reactivity with the solder or the deposit is suppressed, The lead frame material and the solder are less likely to adhere, and the step of removing the adhered matter is not required, which enables long-term use.

The surface of the mold bending portion is JIS B060
10 point average maximum height roughness (Rz) according to 1 is 1 μm
If it is below, the adhesion of solder or the like can be further suppressed. It is considered that this is because the cemented carbide material having a high Young's modulus and a high hardness characteristic remarkably develops the difficulty of adhesion of the cemented carbide material by suppressing the aggressiveness to the leads and the solder plating. Depending on the surface condition of leads and solder plating, if the surface roughness Rz of the cemented carbide die surface is 0.5 μm or less,
Adhesion of plating due to sliding of the lead and the mold during shaping is further suppressed, which is preferable.

More preferably, the cemented carbide material has a three-point bending strength of 30 according to JIS R1601.
If it is 0 Kg / mm ² or more, the present invention can be more remarkable. Since a high load such as impact acts on the mold during processing, high strength is required as a mold material. Therefore, the bending strength is 300 Kg / mm ² or more, so the load applied to the mold It is effective in resisting damage and damage during bending.

When a hard carbon film having a film thickness of 0.1 to 5 μm is formed on the surface of the processed portion made of a cemented carbide material in order to suppress the adhesion of leads and solder during bending, the adhesion suppressing effect is further enhanced. . Here, the hard carbon film refers to a diamond film, a diamond-like carbon film (DLC), an amorphous carbon film (a-C, a-C: H, i-C, etc.). The hard carbon film has excellent slipperiness during shaping and is unlikely to adhere to lead materials or metals such as solder, and the film surface has very high smoothness and is hard to wear, so there is very little loss of smoothness. It is considered that the effect of suppressing adhesion is further enhanced.

When the film thickness is 0.1 μm or less, there is a problem in durability during shaping, and when the film thickness is 5 μm or more, the dimensional accuracy during film formation becomes difficult and the film formation requires a long time. Unfit In order to suppress adhesion to leads and solder by film formation, it is desirable that the surface after film formation has a 10-point average maximum height roughness of 1 μm or less, and more preferably 0.5 μm or less. In order to obtain the above-mentioned surface roughness after the film formation, it may be achieved by a method for forming a hard carbon film, but the surface roughness of the base cemented carbide is 10 μm in average maximum height roughness of 1 μm or less, More preferably, it is desirable to form a film on the surface of 0.5 μm or less.

This is preferable because the surface roughness of the base material is specified to improve the adhesion force during film formation, and the problem of peeling of the film during bending is further improved. As a base material for forming a hard carbon film, the above-mentioned average crystal grain size is mainly 1 μm.
The average thickness of the binder phase, for example, Co phase, is 0.15 μm.
Any cemented carbide material may be used as long as it is m or less.

[0016]

EXAMPLES Next, the effects of the present invention will be specifically described by way of examples. In the following examples, the composition of the cemented carbide material was measured by energy dispersive X-ray spectroscopy (ED
X) By analysis, the average grain size of hard carbides including WC and the average thickness of Co phase are observed by a scanning electron microscope (SEM), and from the contrast of the secondary electron image obtained at that time, the cemented carbide is obtained. The components are discriminated, the average particle size and the average thickness of the Co phase are measured, and the average value is taken.

(Example) The cemented carbide base material according to the present invention was evaluated for adhesion to solder plating. As a method for producing the cemented carbide material, a WC having a size of 1 μm or less is directly produced from a predetermined mixture of fine particles W and carbon in a carbonization furnace, and a predetermined amount of Co is mixed therein, and 0.5 to ² T / cm ² It is molded and sintered in vacuum at about 1300 to 1450 ° C. for 1 hour. Further, a hot isostatic pressing (HIP) process was performed at 1200 to 1350 ° C. to 1000 atm to produce a cemented carbide material having fine particles and high toughness. As the evaluation method, the amount of ball abrasion after the ball-on-disk sliding test shown in FIG. 1 was used.

The ball-on-disk sliding test is performed on a disk (flat plate) which rotates at a rotation speed w as shown in FIG.
The ball is pressed against the load P and the wear phenomenon at that time is examined. For the purpose of evaluating the adhesion to solder plating, a ball having a surface of SUJ-2 ball of 6 mm and 20 μm plating (Pb: Sn = 9: 1) was used for the ball, and samples 1 to 20 and a disk were used. Comparative Examples 1 and 2 were used. Specific sliding conditions are room temperature and atmospheric atmosphere, load 1N, sliding speed 6 m / min, sliding distance 20.
m and sliding circle of 4 mm.

As can be seen from Table 1, the cemented carbide is mainly composed of WC and TiC having an average crystal grain size of 1 μm or less, and the average thickness of the metallic Co phase as the binder phase is 0.1.
When the thickness is 5 μm or less, the amount of deposited plating is half or less as compared with Comparative Examples and those outside the above range, which is preferable. further,
It can be understood from Table 1 that, as a matter of course, when the surface roughness is improved, the plating adhesion amount is reduced, and the 10-point average maximum height roughness (Rz) according to JIS B0601 is preferably 1 μm or less.

[0020]

[Table 1]

Example In this example, a base material was prepared in the same manner as in the above-mentioned example, and samples 21 to 33 in which a hard carbon film was provided on the surface of the base material shown in Table 2 were prepared. Here, sample 34 does not have a hard carbon film for comparison. As a method for forming a hard carbon film, a plasma CVD (chemical vapor deposition) method using glow discharge plasma with high frequency or direct current power, a microwave plasma CVD method, an ion beam vapor deposition method using an ion beam of hydrocarbon gas are used. PVD (physical vapor deposition) methods such as ion plating utilizing sublimation and precipitation of solid carbon are already known. Either method can be used to form the hard carbon film on the lead frame bending die according to the present invention.
In this embodiment, the high frequency plasma CVD method is used.

Now, the method for producing the hard carbon film according to the present invention is as follows. First, the surface to be coated with the cemented carbide material shown in the embodiment, which is the base material, is polished and lapped to a predetermined surface roughness. The surface roughness at this time is preferably 1 μm or less in terms of 10-point average maximum height roughness (Rz). This cemented carbide base material is washed with an organic solvent, detergent, water or the like to prevent any inorganic or organic stains from remaining on the surface. The cleaned cemented carbide substrate is attached to the electrode 12 in the hard carbon film forming apparatus shown in FIG. The inside of the vacuum container 11 is 5 × 1 by the vacuum exhaust device 3.
Evacuated to 0 ^over 6 Torr, then, 0.2Tor argon gas (Ar) into the vacuum container 11 from the gas supply system 14
It is introduced until the degree of vacuum reaches r.

Next, the high frequency (1
(3.56 MHz) Using a power source, 500 W is applied to the electrode 12 to generate discharge, and the surface of the cemented carbide base material 16 is cleaned. After performing ion cleaning for 10 minutes, the high frequency power supply is once stopped, and methane gas (CH ₄ ) is introduced from the gas supply system 14 into the vacuum container 11. When introducing methane gas, vacuum container 11 after stopping argon gas
Pressure of the inner is introduced from becoming below 10 ^@ 6 Torr,
It is introduced until a vacuum degree of 0.2 Torr is reached. After that, 400 W is applied to the electrode 12 by using a high frequency power source to discharge,
A hard carbon film was formed.

In this way, the overall film thickness of 0.08 to 6 μm (S of the cross section is measured by the plasma CVD method using high frequency discharge.
A hard carbon film (confirmed by EM observation) was obtained. For comparison, test pieces having a titanium nitride film and a chromium nitride film formed by the PVD method were prepared and evaluated by a ball-on-disk sliding test similar to that shown in the examples. The evaluation results are shown in Table 2.

[0025]

[Table 2]

As can be seen from Table 2, by providing the hard carbon film, the coating amount is significantly improved as compared with the comparative example of the uncoated cemented carbide base material. However, if the film thickness is 0.1 μm or less, no effect is exhibited. More preferably, when the surface roughness of the substrate before forming the hard carbon film is 1 μm or more in Rz, film peeling occurs. Therefore, it may be judged from the plating adhesion amount that Rz is preferably 0.5 μm. Further, if the surface roughness Rz of the cemented carbide base material is 0.2 μm or less, the adhesion of the hard carbon film is improved, which is preferable. The adhesion strength evaluation here is the result of acoustic (AF) measurement. Further, if the average spacing of the WC phase is 0.15 μm or less, the WC crystal grains are finely dispersed on the surface of the cemented carbide, so Co
The phase becomes thin. The present inventors have found that this contributes to the improvement of the hard carbon film, and have solved the insufficient adhesion between the hard carbon film and the cemented carbide base material, which has been a problem in the past.

(Example) Samples 20, 7, 12 in Table 1
Samples 35, 36 and 3 in Table 3 using the materials
7 in Table 3 using 12 materials in Table 1 and a hard carbon film.
A bending die for a lead frame shown by sample 38 in the inside was prepared and bending was performed. The samples 36 and 37 of the present invention are
The life of the sample 35 was 1.5 times that of the comparative example 5 (conventional material), but the tip of the processed portion was chipped off with the same life as the comparative example 5. Further, in the mold sample 38 provided with the hard carbon film, no plating adhered even when the processing was performed three times as much as that of Comparative Example 5. From the above, the bending strength is JIS
Three-point bending strength according to R1601, 300 Kg / m
When it is m ² or more, damage during processing can be prevented, and further, by providing the hard carbon film, the life of the lead frame bending die can be extended.

[0028]

[Table 3]

[0029]

As described above, by using the mold of the present invention, the present invention is to attach the lead material and the like to the mold for bending the leads in the process of assembling and processing the semiconductor lead frame. It is possible to improve productivity by suppressing adhesion or extending wear life by improving wear resistance, and by extending the cycle lead time of the removal process that occurs to remove the above-mentioned adhered and adhered substances. Become.

[Brief description of drawings]

FIG. 1 shows a ball-on-disk sliding test device.

FIG. 2 shows an apparatus for forming a hard carbon film.

[Explanation of symbols]

 11: Vacuum container 12: Electrode 13: Vacuum exhaust device 14: Gas supply system 15: High frequency power supply 16: Cemented carbide base material

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Go Yoshioka 1-1-1 Kunyokita, Itami City, Hyogo Prefecture Sumitomo Electric Industries, Ltd. Itami Works

Claims (4)

[Claims] 1. A mold for processing a lead frame having a semiconductor chip mounted, wherein at least the processed portion is made of a cemented carbide material, and the cemented carbide material has an average crystal grain size of 1 μm or less. Composed of F
A cemented carbide die for lead frame bending, wherein the average thickness of the binder phase composed of one or more selected from e, Co, and Ni is 0.15 μm or less. 2. The surface of the processed portion made of cemented carbide material is J
The 10-point average maximum height roughness conforming to IS B0601 is 1 μm or less, and the lead frame bending cemented carbide mold according to claim 1. 3. The bending strength of the cemented carbide material is JIS R
Three-point bending strength according to 1601 is 300 Kg / mm ²
The above is the cemented carbide mold for bending a lead frame according to claim 1 or 2. 4. The lead frame bending process according to claim 1, wherein a hard carbon film having a film thickness of 0.1 to 5 μm is provided on the surface of the processed portion made of a cemented carbide material. Mold made of cemented carbide.