JP3438420B2 - Partial plating equipment - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention belongs to the technical field of partial plating, and more particularly to the technical field of a partial plating apparatus suitable for partial electroplating on a wire bonding portion of a lead frame of a semiconductor element.

[0002]

2. Description of the Related Art As a conventional partial plating apparatus, there is one disclosed in JP-A-4-346691.
The main part of this device is composed of a sparger, a rubber control plate mounted on the sparger, and a mask sponge for pressing the material to be plated mounted on the rubber control plate. An opening is provided on the upper surface of the sparger, and the plating solution is supplied to the material to be plated facing the opening from the inside of the sparger.

A typical example of the material to be plated is a lead frame of a semiconductor element, which has a plate shape or a substantially plate shape. A penetrating portion that communicates with the opening of the sparger is formed between the lead frames. The mask sponge is pressed against the material to be plated with a pressing force, and sandwiches the material to be plated with the sparger covered with the rubber control plate. The mask sponge penetrates the through-hole of the material to be plated, covers the lead frame, and masks the portion that should not be plated. The mask sponge is made of neoprene rubber or the like, and its hardness is not specified in detail.

In this apparatus, the plating solution is supplied from the inside of the sparger to the material to be plated through the opening, and the plating layer is formed on the portion which is not masked by the mask sponge to carry out the partial plating treatment.

[0005]

In the above-described conventional partial plating apparatus, the following problems may occur in the non-plated part. The defect is the generation of plated metal particles that occur between a plurality of plated portions that are close to each other. For example, in a partial silver plating apparatus for a lead frame, as shown in FIG. 4, the precipitation of silver particles G between adjacent leads F is the problem. (FIG. 4 is a sketch based on a photograph taken by cutting the deposited portion of the silver particles that actually occurred in the conventional technique.) Since the defect due to the generation of the plated metal particles causes a short circuit between the lead frames, This is a serious obstacle in reducing the pitch of the lead frame spacing accompanying the miniaturization and high integration of electronic products such as semiconductor devices.

Further, in the conventional partial plating apparatus, a defect called out-of-area precipitation may occur. As shown in FIG. 6, the out-of-area deposition means that the plating layer P penetrates from the plating area to be plated into a part of the area that is originally masked and should not be plated. If there is precipitation outside the area, for example, in a lead frame of a semiconductor device packaged in a small package, the margin for the package area will be lost, and the plated portion will extend to the outside of the package area. As a result, the plating squeezes out (deposits outside the area) during long-term application of voltage.
Electromigration occurs in a portion, which eventually causes a short circuit. Further, since the consumption of the plating solution increases, there is a disadvantage that the cost of the partial plating process increases.

[0007] Therefore, an object of the present invention is to provide a partial plating apparatus which prevents partial plating defects such as generation of plated metal particles between portions to be plated (penetrating portions).

[0008]

According to a first aspect of the present invention, a sparger having an opening to which a plating solution is supplied from the inside and a plate-shaped material to be plated having a penetrating portion are sandwiched together with the sparger, and the penetration is performed. A partial plating apparatus having a mask sponge covering a portion, wherein the mask sponge is made of foamed silicone rubber and is in contact with the material to be plated.
Conductivity contained near the contact surface of the mask sponge
Among the impurities, Si and Pb are the thickness from the contact surface.
Per unit area of the relevant contact surface for parts up to 1 cm
0.3 [mg / cm ² ] or less and 0.01, respectively
The partial plating apparatus is characterized in that it is [mg / cm ² ] or less .

A second structure of the present invention is further characterized in that, in the first structure, the mask sponge has a rubber hardness of 12 degrees or more and 16 degrees or less. Here, the hardness standard is a hardness standard that is standardly used in the rubber industry and the sponge industry (Japan Rubber Association Standard SRIS
0101, Asker C type hardness meter according to JIS S 6050).

[0010]

[0011]

In the first structure of the present invention, since the mask sponge is made of foamed silicone rubber having high electric insulation, a negative charge that attracts metal ions in the plating solution is generated on the surface of the mask sponge. Or it does not stay (or is extremely low). Therefore, according to this configuration, the plating metal particles are prevented from depositing on the surface of the mask sponge between the plated portions such as the lead frame. Therefore, a short circuit between portions to be plated is less likely to occur, and there is an effect that finer partial plating can be performed. In addition, the conductivity near the contact surface of the mask sponge
Since the content of volatile impurities is quantitatively limited,
The contact surface of the mask sponge with high electrical insulation is formed.
It Therefore, according to this configuration, the plating is further enhanced.
Generation of metal particles is suppressed, and finer and finer parts
It has the effect of making it possible.

In the second structure of the present invention, since the rubber hardness of the mask sponge is further limited to 12 degrees or more and 16 degrees or less, the mask sponge is appropriately filled between the lead frames having a narrow pitch as the material to be plated. It That is, it is possible to avoid the problem that the mask sponge is too hard to be sufficiently filled between the lead frames, resulting in a gap and insufficient masking. Conversely, the mask sponge is too soft and dives between the leadframes and protrudes to the opposite side, and even a part of the part to be plated is masked and a sufficient plating film is not formed (surface part not attached). , Are avoided at the same time.

Therefore, according to this structure, there is an effect that the deposition outside the area and the defect that the surface portion is not adhered can be prevented. As a result, not only is it possible to perform partial plating with higher accuracy, but there is no consumption of extra plating solution, which also contributes to cost reduction.

[0014]

[0015]

[Example 1]

(Apparatus configuration of Example 1) As shown in FIG. 1, a partial plating apparatus as Example 1 of the present invention has a lower half B fixed to a base (not shown) and a supporting member above it. (Not shown) and an upper half portion A slidably held up and down.

The main part of the lower half B is a sparger 1 at its upper end and a rubber control plate 2 made of silicon rubber mounted on a rectangular horizontal surface 11 formed at the upper end of the sparger 1.
It consists of On the center line along the long side of the horizontal surface 11 of the sparger 1, a plurality of rectangular openings 10 are formed at regular intervals. The rubber control plate 2 also has a sparger 1
A plurality of rectangular openings 20 are formed so as to correspond to the openings 10 of FIG.

The main part of the upper half A is a mask sponge 3 having a contact surface 31 facing the horizontal surface 21 of the rubber control plate 2 forming the upper surface of the lower half B, and the contact surface 3 of the mask sponge 3.
1 and an upper mold 4 for fixing and holding the mask sponge 3 on the upper plane facing back. The upper half portion A further includes an elevating plate 5 that holds the upper die 4 from above and a supporting column 51 that holds the elevating plate 5 slidably in the vertical direction.

A lead frame F (not shown) as a material to be plated is placed on the horizontal surface 21 of the rubber control plate 2 on the sparger 1 in a state where one or a plurality of lead frames F are connected in series. At that time, at least one positioning pin 12 protruding from the horizontal surface 11 of the sparger 1 is fitted into a positioning hole (not shown) provided in the lead frame F. Further, the lead frame F is accurately positioned by the plurality of guide pins 13 that vertically project from the horizontal surface 11 of the sparger 1.

As a result, the connected lead frame F is precisely installed at the position shown by the broken line F'in FIG. At the same time, the lead frame F to be partially plated
And the through portion thereof is accurately installed on the openings 10 and 20 to prepare for the partial plating process. The upper half portion A vertically descends from above the rubber control plate 2 on the sparger 1 on which the lead frame F is placed to the inside of the guide pin 13 and the positioning pin 12, and contacts the contact surface 31 on the lower surface of the mask sponge 3.
Contacts the lead frame F and the horizontal surface 21 on the rubber control plate 2 around it with an appropriate pressing force. As a result, the lead frame F has its penetrating portion covered with the mask sponge 3 and the mask sponge 3 and the rubber control plate 2.
It is sandwiched between and in the correct position, and the plating process is ready.

At this time, the pressing force of the mask sponge 3 is 3.0 as an average value per unit area of the contact surface 31.
It was [kgf / cm ² ]. (Partial Plating Treatment of First Embodiment) Next, a partial plating treatment by the partial plating apparatus of the present embodiment will be described with reference to FIG. 2 schematically showing the configuration.

The partial plating apparatus of the present invention basically comprises
It is composed of a sparger 1 to which the plating solution L is supplied from the inside, a rubber control plate 2 and a mask sponge 3 for pressing and holding a lead frame F as a material to be plated. The opening 10 of the sparger 1 has a plating solution L containing silver ions from the inside.
Are circulated and blown by a pump (not shown). That is, the plating solution L is sprayed onto the lead frame F facing the opening 10 by containing the positively charged silver ions by the anode 6 having a through hole formed in the center thereof. After that, the plating solution L is circulated and sprayed again on the lead frame F after the contaminants are removed by the filter 8.

On the other hand, an electric wire 7 is connected to the back side of the lead frame F (the side facing the sparger 1),
The lead frame F itself forms the negative electrode. Therefore, silver ions having a positive charge are deposited on the portions of the lead frame F that are not masked by the rubber control plate 2 and the mask sponge 3, and the partial plating treatment is performed. (Mask Sponge of First Embodiment) In the partial plating apparatus of the first embodiment, the mask sponge 3 is a plate material having a rectangular plane shape with a thickness of 10 mm and formed of foamed silicone rubber, and its hardness is 12 to 16 degrees. Up to.

It was also confirmed that among the conductive impurities contained near the contact surface 31 of the mask sponge 3, Si and Pb were sufficiently small. That is, as a result of washing the mask sponge 3 in a KOH aqueous solution (50 g per liter) and analyzing the solution by atomic absorption, the main impurities were Si and Pb. The content is 0.3 [mg / cm ² ] of Si per unit area of the contact surface 31.
It was revealed that Pb was 0.01 [mg / cm ² ] or less.

The content of the conductive impurities used in the present specification is determined by carrying out an atomic absorption analysis of the solution after washing with KOH aqueous solution (50 g per liter) as described above. Are changing. The mask sponge 3 made of foamed silicone rubber was prepared by changing the hardness from 12 degrees to 16 degrees in steps of 1 degree. For each mask sponge 3 of each hardness, at least three mask sponges 3
Partial plating treatment was performed on 00 or more samples (lead frames) by the partial plating apparatus described above.

As a result, very good results were recorded, with 0% silver grain precipitation failure and 0% out-of-area growth failure.
Therefore, according to the partial plating apparatus of the present embodiment, it is possible to effectively prevent a defect due to the deposition of silver particles as plated metal particles and a defect due to the out-of-area growth of the plating layer. For reference, a plan view of the lead frame F as a material to be plated is shown in FIG. Several black-painted portions (inside the rectangular area) in the figure are the portions of the lead frame to be plated. It can be seen from FIG. 3 that through-holes are formed between the lead frames to be partially plated and that a plurality of alignment holes F0 are formed in the peripheral edge of the lead frame F.

The thickness of the single lead wire of the lead frame F is about 250 μm, and the width of the single lead wire is about 20 at the narrowest portion.
0 μm, spacing between adjacent leads is about 200 μ at the narrowest part
m. By the way, sparger 1 of lead frame F
The thickness of the silver-plated layer on the surface to be plated facing the opening 10 was about 5 μm as a standard. Furthermore, the minimum diameter of silver particles that can be detected was about 10 μm, and the allowable width from the plating area to the maximum plating area, which was the criterion for precipitation outside the area, was about 400 μm.

Further, the lead frame F has already been mass-produced in the above hardness range, and has already been produced in the unit of ten thousand. There is no case. Therefore, it can be said that the present invention is no longer at the laboratory level and has been completed as a technique applicable to mass production. By the way, for the purpose of clarifying the difference between the partial plating apparatus of the present embodiment and the partial plating apparatuses of other embodiments and the prior art, a plurality of mask sponges having different materials and hardness from those of the present embodiment were manufactured. . Then, a partial plating apparatus equipped with these mask sponges was subjected to partial plating treatment on the same lead frame F as the material to be plated in this example for evaluation, which will be described below.

Example 2 The mask sponge was made of foamed silicone rubber as in Example 1, but the hardness of the mask sponge was 17 degrees. Other parts were subjected to partial plating under the same conditions using the same lead frame F as the material to be plated in the same partial plating apparatus as in Example 1 to obtain a plurality of comparative samples.

As a result, there was no silver grain defect, but the out-of-area precipitation defect occurred at a rate of about 1%. Therefore, by forming the mask sponge from foamed silicon rubber, defects due to the precipitation of silver particles can be completely prevented, but if the hardness of the mask sponge exceeds 16 degrees, the prevention of deposition defects outside the area is not complete. It became clear.

(Example 3) A mask sponge having a hardness of 11 degrees was manufactured by using the same material as foamed silicone rubber. Then, a partial plating treatment was performed in the same manner as in Example 2 to obtain a plurality of comparative samples. As a result, there was absolutely no silver grain defect or out-of-area precipitation defect, but plating part non-adhesion defect occurred at a rate of about 1%. Here, the non-deposited plating portion means that the plating layer is not formed on at least a part of the portion to be plated.

Therefore, by using the mask sponge formed of foamed silicone rubber having a hardness of 11 degrees, defects due to the precipitation of silver particles and defects outside the area can be completely prevented. However, if the hardness of the mask sponge is less than 12 degrees, it may become inconvenient because the defective plating may not be adhered. (Comparative Example 1) Using a mask sponge made of a natural rubber foam having a hardness in the range of 12 to 16 degrees in steps of 1 degree, a partial plating treatment was similarly performed to obtain a plurality of comparative samples. Si and Pb contained in the vicinity of the contact surface of the mask sponge were 0.3 [mg / cm ² ] or less and 0.01 [mg / cm ² ] respectively by the same method for measuring the content of conductive impurities as in Example 1. cm ² ] or less.

As a result, the effect of the sponge material containing a small amount of conductive impurities was confirmed without any defective silver particles or defective deposition outside the area. However, discoloration of the plating occurred when the partial plating treatment was performed at a low current. The discoloration of the plating causes a defect such as a decrease in the adhesion of wire bonds performed for the purpose of electrically connecting the IC chip and the lead frame, which is performed in a later step, and is one of the plating defects, and is preferable. Absent.

Therefore, with the mask sponge made of natural foamed rubber having a small content of conductive impurities and having an appropriate hardness, defects due to the precipitation of silver particles and defects outside the area can be prevented, but a defect such as discoloration of the plating. It has become clear that will happen. The inventors presume that the cause of the discoloration of the plating is the coloring caused by the dissolution and adhesion of the organic matter contained in the mask sponge.

(Comparative Example 2) A mask sponge having the same hardness and conductive impurity content as in Comparative Example 1 was used, and the same partial plating treatment was carried out to obtain a plurality of comparative samples. However, the material of this mask sponge is urethane foam. As a result, similar to Comparative Example 1, although there was no silver grain defect or out-of-area precipitation defect, discoloration of the plating occurred, which was inconvenient.

(Conclusion of Example 1) The following conclusions can be drawn by comparing the test results and results of Example 1 described above with the test results of Examples 2 and 3 and Comparative Examples 1 and 2. That is, in the partial plating apparatus using the foamed silicone rubber of Example 1, none of the defects of plating defects due to precipitation of silver particles between leads, defective deposition outside the area, and discoloration of plating did not occur. Therefore, according to the partial plating apparatus of the present embodiment, it is possible to perform extremely excellent partial plating on a material to be plated which is fine such as the lead frame F.

As a result, according to the present invention, the pitch of the lead frame F or the like can be narrowed, and it is possible to provide a partial plating apparatus which is sufficiently compatible with further miniaturization and miniaturization of electronic parts including semiconductor elements and the like. . Further, according to the partial plating apparatus of the present embodiment, wasteful consumption of silver is eliminated,
Since the defective product rate due to defective plating is reduced, there is also an effect of cost reduction.

(Discussion on Silver Grain Deposition Failure) The inventors conducted a detailed comparative examination of the above-mentioned Examples 1 to 3 and Comparative Examples 1 and 2 to find out the silver grain deposition which occurred in the conventional partial plating apparatus. The cause of the defect was considered. As a result, as shown in FIGS. 5A and 5B, it was estimated that the conductivity of the mask sponge 3 was responsible.

That is, if the mask sponge 3 has a slight conductivity due to the fact that the mask sponge 3 contains conductive impurities, as shown in FIG.
It is electrically attracted to the anode 6 and negative charges are concentrated near the surface of the contact surface 31. (Because a predetermined potential difference is applied between the anode 6 and the conducting wire 71, the negative charge is
Supplied from Then, the positively charged silver ions Ag in the plating solution L are adsorbed and deposited on the contact surface 31.

At the end of the partial plating process, as shown in FIG. 5B, the silver is formed on the surface of the contact surface 31 of the mask sponge 3 between the leads F on which the silver plating layer P is formed. It is presumed that the grain G grows to cause plating failure due to the generation of silver grains. Therefore, when the mask sponge 3 is made of foamed silicone rubber having an extremely excellent insulating property, it is considered that negative charges do not collect on the contact surface 31 and the defective generation of silver particles is prevented. To be

Similarly, even when the mask sponge 3 is formed of a foamed material of natural rubber or urethane, if the content of the conductive impurities such as Si and Pb is suppressed to a predetermined amount or less, it is similar to some extent. It is thought that the effect can be obtained. However, if the mask sponge is formed of a material other than silicone rubber, plating defects such as discoloration of the plating tend to occur, so a partial plating apparatus using the foamed silicone rubber mask sponge 3 of the present invention should be used. It does not reach.

Incidentally, in addition to the idea that the silver sponge generation defect occurs due to the conductivity of the mask sponge 3 as described above, there is also the cause of the silver grain generation defect.
For example, due to various characteristics of the contact surface 31 of the mask sponge 3 (water repellency, fine unevenness, affinity with silver, etc.),
There is a possibility that it may affect whether or not the precipitation of silver particles begins.

That is, the cause of defective generation of silver particles is
There is an idea that the surface characteristics of the contact surface 31 are dominant, but it is not clear yet. (When water repellency is a dominant factor in the surface characteristics of the contact surface 31, the mask sponge 3 having the contact surface 31 that has been subjected to a water repellent treatment such as application of a water repellent is adopted. It may be an effective means for preventing defective generation of silver grains.) (Consideration regarding growth defect outside area) As shown in FIG. 6, the deposition outside the area exceeds the plating area to be plated, and further plating is allowed. This is a phenomenon in which a plating layer is formed beyond the maximum plating area, which is the maximum range of

The cause is that the mask sponge 3 has an excessive hardness, and depending on a predetermined pressing force, as shown in the lower half of FIG. 7C, even outside the plating area other than the sparger 1 opening, This is because the mask sponge 3 does not sufficiently wrap around between the leads F. That is, since a gap g is formed between the contact surface 31 of the mask sponge 3 and the rubber control plate 2 on the sparger 1 to allow the infiltration of the plating solution, deposition outside the area occurs.

On the contrary, if the hardness of the mask sponge 3 is too small, as shown in the upper half of FIG. 7A, a part 32 of the contact surface 31 projects laterally in the drawing and the lead to be plated. It will cover the face of F. As a result, the plating solution does not circulate in the covered portion of the lead F, and the plating layer is not formed. Therefore, the upper limit of the hardness of the mask sponge 3 is determined by the deposition outside the area, and conversely, the lower limit thereof is determined by the defective adhesion of the plated portion. Thus, the proper hardness of the mask sponge 3 is naturally limited to 12 degrees or more and 16 degrees or less. When the hardness of the mask sponge 3 is within the proper range, the condition shown in FIG.
As shown in (4), appropriate masking is performed to prevent deposition outside the area and defective adhesion of the plated portion.

(Modification of Embodiment 1) In this embodiment, the partial plating apparatus for performing the partial silver plating on the lead frame F has been described, but the partial plating apparatus of the present invention is not limited to this. . That is, the plating solution is not limited to silver plating, and may be a known plating solution containing gold, platinum, other metal or alloy. Further, the material to be plated is not limited to the lead frame F, and the present invention can be applied to a material to be plated that requires any partial plating. Furthermore, the present invention is not limited to electroplating, and the present invention can be applied to chemical plating, vapor phase plating, etc. as long as it is partial plating requiring masking.

[Brief description of drawings]

FIG. 1 is a perspective view of a main part showing a structure of a partial plating apparatus according to a first embodiment.

FIG. 2 is a schematic diagram showing the operation of the partial plating apparatus of Example 1.

FIG. 3 is a plan view showing the shape of a lead frame (state after partial plating treatment) as a material to be plated.

FIG. 4 is an end view showing defective silver particles generated between leads.

FIG. 5 is an end view schematically showing a mechanism of occurrence of defective silver particles. (A) Initial state of partial plating treatment (B) Termination status of partial plating

FIG. 6 is a perspective view schematically showing an out-of-area precipitation defect that has occurred on a lead.

FIG. 7 is a schematic diagram showing the hardness and masking state of the mask sponge. (A) When the mask sponge has an excessively low hardness (b) When the mask sponge has an appropriate hardness (c) The mask sponge has an excessively high hardness If

[Explanation of Codes] 1: Sparger 10: Opening 11: Horizontal plane 2: Rubber control plate 20: Opening 21: Horizontal plane 3: Mask sponge 31: Contact surface 32: Overhanging 4: Upper mold 6: Anode 7, 71: Electric wire, Conductor (cathode side) F: Lead frame, lead (material to be plated) G: Silver particles L: Plating solution P: Silver plating layer

Front page continued (72) Inventor Yoshihiko Mizutani, 1-1, Showa-cho, Kariya city, Aichi Prefecture, Japan Denso Co., Ltd. (72) Inventor, Kumiko Ono, 1-1, Showa-cho, Kariya city, Aichi prefecture, Nippon Denso Co., Ltd. (56 ) Reference JP 62-263992 (JP, A) JP 62-163353 (JP, A) JP 60-255992 (JP, A) JP 59-85888 (JP, A) JP 59-85887 (JP, A) JP 52-71343 (JP, A) Actual development 62-135446 (JP, U) Actual development 62-75066 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) C25D 5/02 H01L 23/50

Claims (2)

(57) [Claims] 1. A partial plating apparatus comprising: a sparger having an opening to which a plating solution is supplied from the inside; and a mask sponge for sandwiching a plate-shaped object to be plated having a penetrating portion together with the sparger and covering the penetrating portion. The mask sponge is made of foamed silicone rubber ,
And, of the mask sponge that contacts the material to be plated
Of the conductive impurities contained near the contact surface, Si and
And Pb are for the part up to 1 cm thick from the contact surface.
And 0.3 [mg / per unit area of the contact surface
cm ² ] or less and 0.01 [mg / cm ² ] or less
That, the partial plating system, characterized in that. 2. The mask sponge is 12 degrees or more and 16 degrees or more.
The partial plating apparatus according to claim 1, which has a rubber hardness of not more than 100 degrees.