JP2001230531A - Method of mounting electronic component - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of mounting an electronic component which is superior in bonding reliability. SOLUTION: A solder precoating layer is formed on a bonding pad for mounting component with a BVH structure of a mother board. Subsequently, after the solder is precipitated, electronic components are mounted on the mother board.

Description

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a method for mounting an electronic component on a motherboard.

[0002]

2. Description of the Related Art In recent years, the use range of terminal components used for information equipment and peripheral devices has been dramatically increased with the expansion of economic activities. The printed circuit boards used for these devices and components are required to be smaller and lighter in nature, and the density and size of semiconductor mounting pads mounted on the printed circuit boards are required. As a technology for responding to such high density and miniaturization of semiconductor components, a technology for improving reliability in connection strength between a motherboard and a package component has been required.

Further, a build-up multi-layer wiring board is effective as a board corresponding to high density and miniaturization of semiconductor components. However, since the CSP / BGA connection pad of the BVH structure in the build-up multilayer wiring board has an indented portion, bubbles may be generated at the connection portion between the pad and the solder ball due to the structure of the BVH pad. There were many times. Further, these bubbles may cause cracks due to expansion when heated, and eventually cause semiconductor mounted components to fall off the motherboard.

[0004] Therefore, as a substrate preparation technology corresponding to the high density and miniaturization of semiconductor components, a high connection strength technology for preventing mounting components from dropping at solder ball connection portions of a mother board and a solder ball connection portion of a package component, and a BVH structure. At the same time, there is a need for a technology that does not generate air bubbles at the connection points between the solder balls and the solder balls, and a solder application technology that does not generate bridges and the like even for connection pads that have a higher density.

[0005] For example, JP-A-8-204113 discloses a technique for smoothing connection pads having a BVH structure by electroless plating. Also, JP-A-11-1
Japanese Patent No. 91733 discloses a technique for improving connection reliability by using a material other than solder to improve connection strength.

[0006] However, the method disclosed in Japanese Patent Application Laid-Open No. 8-204113 can smooth the connection pad of the BVH structure, but has a feature in the field of improvement in connection strength with solder balls and improvement in reliability. Not. Further, a connection strength technology as disclosed in Japanese Patent Application Laid-Open No.
BVH is effective for the smooth pad part without the structure.
CSP / B with mixed structure and smooth pad with BVH structure
There is no description for use in a pad for mounting a GA, and it is difficult to apply to a high-density substrate using a large number of BVH structures due to advantages in design and the like. Therefore, as connection reliability technologies that can respond to miniaturization of semiconductor mounted components, high connection strength technology that does not cause the mounted components to fall off, technology that does not generate air bubbles at the connection points between the BVH structure and the solder balls, and connection pads that have higher densities As a matter of fact, there is still no sufficient method that can cope with a solder coating technique that does not generate a bridge or the like.

[0007]

SUMMARY OF THE INVENTION The present invention has been made to solve such a situation, that is, the problem of the CSP / BGA connection reliability technology as shown above. It is an object of the present invention to provide a method for mounting an electronic component having excellent CSP / BGA bonding reliability by improving the connection strength between a motherboard and a package component in a built-up multilayer wiring board.

[0008]

Means for Solving the Problems The present inventors have conducted various studies to achieve the above object. As a result, as connection reliability technology that can respond to miniaturization of semiconductor mounted components,
Supports high connection strength technology that does not drop mounted components, technology that does not generate air bubbles at the connection point of BVH training and solder balls, and solder application technology that does not generate bridges etc. even for higher density connection pads Has found that it is extremely effective to perform a solder pre-coating process on a bonding pad portion for a mounted component, and has completed the present invention.

That is, the present invention relates to a motherboard BVH.
The above object has been achieved by forming a solder precoat layer on a bonding pad portion for a mounting component having a structure, depositing solder, and then mounting an electronic component on the motherboard.

The present invention also provides a method for forming a solder precoat layer on both a bonding pad portion for a mounting component having a BVH structure and a bonding pad portion for a mounting component having no BVH structure on a mother board, and then depositing solder. The above object has been achieved by mounting electronic components on the motherboard.

Further, the present invention provides a solder pre-coat layer formed on both a bonding pad portion for a mounting component having a BVH structure of a motherboard and a bonding pad portion for a mounting component of an electronic component, and then deposits solder, and then deposits the solder. The above object has been achieved by mounting the electronic component on a motherboard.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, it is desirable to perform plating on the bonding pad portion for mounting components before forming the solder precoat layer from the viewpoint of preventing oxidation and corrosion of the connection pad portion. As the plating treatment, for example, an electroless Ni / Au plating treatment is preferably mentioned.

The solder precoat layer according to the present invention is formed using a solder paste containing organic acid lead and tin as main components, particularly a solder paste containing 25% by weight of organic acid lead and 33% by weight of tin. Is particularly advantageous. The solder paste composed of the organic acid lead and tin causes a chemical reaction to proceed in a reflow process. That is, 200 in the reflow process
First, in the solder paste heated to about 250 ° C., lead ions of the organic acid lead are ionized by heat. Next, a part of the lead ions undergoes a substitution reaction with nickel on the underlying nickel surface, and a thin layer of lead is formed on the nickel surface. In addition, most of the lead ions undergo a substitution reaction with tin and precipitate as a single element of lead, and the simple substance mixes with tin and precipitates as solder.

There are two characteristics in this reaction.
One is where a thin layer of lead forms on the nickel surface. Due to this action, the underlying nickel does not come into contact with tin, so it suppresses the diffusion of nickel into tin,
As a result, the segregation of phosphorus is suppressed. The other point is that lead precipitates as a simple substance, and the simple substance mixes with tin to precipitate as a solder. Due to this phenomenon,
Solder is characterized in that it is gradually deposited in the reflow process and is selectively deposited only on the pad surface of the metal portion. Therefore, this feature enables filling of the BVH portion with a voidless.

When a general solder paste made of tin and lead is used, the solder inside the paste is rapidly melted in the reflow process and comes into contact with the BVH portion.
Inner bubbles generated by the dent of H are difficult to escape from the paste,
Voids easily occur in BVH.

The solder precoat layer according to the present invention is formed by applying the above-mentioned solder paste to, for example, a metal mask having a thickness of about 100 to 300 μm, which is opened at a BGA or CSP location on a motherboard which requires high bonding strength. Used and formed by coating such as screen printing.

The thickness of the metal mask is proportional to the amount of solder deposited in the subsequent reflow step, and the thickness of the metal mask is adjusted by the amount of solder to be deposited on the pad. For example, in a solder paste printed by using a 150 μm metal mask, a solder having a height of about 20 to 50 μm is deposited on a flat pad, and about 0 to 30 μm in a pad portion having a BVH structure. Of solder is deposited.
Therefore, the amount of solder deposited on the pad can be controlled by the thickness of the metal mask,
The desired amount of solder can be deposited.

Further, the printed solder paste is:
The solder is deposited by the reflow process as described above.
That is, the motherboard on which the solder paste is printed enters a reflow process and receives heat for about 2 minutes at a temperature of 200 to 250C. The heat is absorbed by the solder paste, and the solder is deposited by the above-described solder deposition mechanism. Further, since the deposited solder is deposited only on the pad of the metal portion, sufficient soldering can be easily performed even on the fine pitch pad portion. After the reflow step, ultrasonic cleaning with warm water or the like is performed.

In the present invention, the mounting of the electronic component on the motherboard after the solder is deposited is performed via solder balls having a general composition.

[0020]

The present invention will be further described with reference to the following examples.

Embodiment 1 FIG. 1 is a schematic process diagram showing a first embodiment of the present invention, which will be described below with reference to FIG. First step Motherboard 1 having solder resist 4
The electroless Ni / Au plating 3 was applied to the bonding pad portion 9 for mounting components having the BVH structure in FIG.
(A)). Second step A solder paste containing 25% by weight of an organic acid salt and 33% by weight of tin is applied to the pad portion 9 plated with 3 in the first step, using a metal mask having a thickness of 100 to 300 µm. Printing was performed by a screen printing method to form a solder precoat layer 5 (FIG. 1B). Third Step The motherboard 1 on which the solder precoat layer 5 has been formed in the second step is subjected to a reflow furnace at 220 ° C. for about 2 hours.
1 minute to deposit solder 6 (FIG. 1).
(C)). Fourth step The motherboard 1 obtained in the third step is
After washing with an alcoholic organic solvent, hot water washing and water washing were further performed. Fifth Step An electronic component (package substrate) 8 is mounted on the pad portion 9 of the mother board 1 cleaned in the fourth step via a solder ball 7 made of tin and lead (FIG. 1).
(D)).

Embodiment 2 FIG. 2 is a schematic process diagram showing a second embodiment of the present invention, which will be described below with reference to FIG. First step Motherboard 1 having solder resist 4
Electroless Ni / Au plating 3 was applied to the bonding copper pad portion 2 for mounting components having no BVH structure and the bonding pad portion 9 for mounting components having a BVH structure in FIG.
(A)). Second Step A solder containing 25% by weight of an organic acid salt and 33% by weight of tin is applied to each of the pad portions 2 and 9 plated with 3 in the first step by using a metal mask having a thickness of 100 to 300 μm. The paste was printed by a screen printing method to form a solder precoat layer 5 (FIG. 2).
(B)). Third Step The motherboard 1 on which the solder precoat layer 5 has been formed in the second step is subjected to a reflow furnace at 220 ° C. for about 2 hours.
2 minutes to deposit solder 6 (FIG. 2).
(C)). Fourth step The motherboard 1 obtained in the third step is
After washing with an alcoholic organic solvent, hot water washing and water washing were further performed. Fifth Step An electronic component (package substrate) 8 is mounted on each of the pad portions 2 and 9 of the mother board 1 cleaned in the fourth step via solder balls 7 made of tin and lead (FIG. 2D). ).

Embodiment 3 FIG. 3 is a schematic process diagram showing a third embodiment of the present invention, which will be described below with reference to FIG. First step Motherboard 1 having solder resist 4
The bonding pad portion 9 for the mounting component having the BVH structure and the bonding copper pad portion 2 for the mounting component in the electronic component (package substrate) 8 in the above-described embodiments are respectively provided with electroless Ni / A.
u plating 3 was applied (FIG. 3A). Second Step A solder containing 25% by weight of an organic acid salt and 33% by weight of tin is applied to each of the pad portions 2 and 9 plated with 3 in the first step by using a metal mask having a thickness of 100 to 300 μm. The paste was printed by a screen printing method to form a solder precoat layer 5 (FIG. 3).
(B)). Third step Mother board 1 and electronic component (package board) on which solder precoat layer 5 is formed in the second step
8 was heated at 220 ° C. for about 2 minutes in a reflow furnace to deposit solder 6 respectively (FIG. 3C). Fourth Step After the motherboard 1 and the electronic component (package board) 8 obtained in the third step were washed with an alcohol-based organic solvent, they were further washed with hot water and water. Fifth Step An electronic component (package substrate) 8 cleaned in the fourth step is mounted on the pad portion 9 of the mother board 1 cleaned in the fourth step via a solder ball 7 made of tin and lead (FIG. 3 (d)).

Comparative Example 1 An electronic component (package substrate) was mounted on a bonding pad portion for a mounting component having a BVH structure on a motherboard in the same manner as in Example 1 except that the solder precoating treatment was not performed.

Test Example 1 Using CPS / BGA mounting pad portions on a motherboard, the bonding strength value was measured with and without solder precoat surface treatment. The bonding strength was measured by a pull test method (manufactured by Daisy Corporation) in which a solder ball was first mounted on a pad portion on a motherboard and then the solder ball was pulled vertically. Pad (pad diameter:
The surface of the 650 μm) portion is electroless Ni / Au plating, and the diameter on the pad is 750 when there is no solder pre-coat.
A μm solder ball was immediately mounted by reflow heat. When there was a solder pre-coat, the solder pre-coat treatment was performed in the same manner as in Example 1, and then the solder balls were mounted in the same manner as described above. Table 1 shows the results.

[0026]

[Table 1]

As is clear from Table 1, the bonding strength between the pad portion and the solder ball was 7.8 N when no solder pre-coating was performed, and 1 when the solder pre-coating was performed.
8.1N. From these results, it was confirmed that the solder precoating process of the present invention was a technique for dramatically improving the bonding strength between the pad portion and the solder ball. Further, it was confirmed that voids were generated in the pad portion having the BVH shape when the solder pre-coating was not performed, and no voids were generated when the solder pre-coating was performed. From this, it has been confirmed that the present invention is effective also in a pad portion having a BVH shape of a build-up multilayer wiring board used as a board corresponding to high density and miniaturization of semiconductor components.

Test Example 2 In order to confirm the effect of the present invention in the mounted state, a package component was mounted on a motherboard via solder balls, and a cooling / heating cycle test was performed on the assumption that the package component was used as a product. The thermal cycle test is -65 ° C (30 minutes) ⇔1
The number of cycles until the conduction resistance value abruptly increases due to cracks at the joint between the pad and the solder, comparing the conduction resistance value in each test state with 25 ° C. (30 minutes) as one cycle number. Were compared. The test was conducted with the motherboard subjected to solder pre-coating as Example 1
Example 2 was a state in which both the motherboard and the package were subjected to solder precoating, and Comparative Example 1 was a state in which both the motherboard and the package were not subjected to the solder precoating and only the plating was performed. Table 2 shows the results.

[0029]

[Table 2]

As is apparent from Table 2, the number of cycles required for the product 1 in which the mother board was subjected to the solder pre-coating process to be abruptly increased in the conduction resistance value was 400 cycles. From this result, it was confirmed that the substrate was in a bonded state having high reliability.

The product 3 in which both the mother board and the package substrate were subjected to the solder pre-coating process had 500 cycles before the conduction resistance value was sharply increased, and particularly excellent bonding with high reliability. The state was confirmed.

The component mounting board of Comparative Example 1, in which both the motherboard and the package board were not subjected to the solder pre-coating process, had 100 cycles before the conduction resistance sharply increased, which was the lowest in the test. It was confirmed that the joint was reliable.

As described above, the remarkable effectiveness of the technique for improving and stabilizing the bonding strength by the solder pre-coating process according to the present invention was confirmed.

[0034]

According to the present invention, since the connection between the motherboard and the electronic components is firm by the solder pre-coating process and the mounted components do not fall off the motherboard, it is possible to obtain a component mounting board having extremely excellent connection reliability. it can.

In particular, if a solder precoat layer is formed using a solder paste containing organic acid lead and tin as main components,
In the process of the reflow furnace, the solder is gradually deposited on the pad portion of the metal surface, so that even in a place having a dent such as a BVH structure, it is possible to perform soldering in a flat state without generating a void. At the same time, fine pitch solder deposition is possible, so that bridges are not generated even in a narrow pitch design, and a board with particularly excellent CSP / BGA connection reliability can be provided.

If Ni / Au plating is performed before the formation of the solder precoat layer, lead ions are generated during the solder deposition process. Since the layer is formed, the lead layer suppresses the diffusion of nickel into the solder layer during hot sensation. As a result, the segregation of phosphorus can be suppressed. Especially strengthened.

[Brief description of the drawings]

FIG. 1 is a schematic process diagram showing a first embodiment of the present invention.

FIG. 2 is a schematic process diagram showing a second embodiment of the present invention.

FIG. 3 is a schematic process diagram showing a third embodiment of the present invention.

[Explanation of symbols]

 1: motherboard 2: pad portion 3: plating 4: solder resist 5: solder precoat layer 6: solder 7: solder ball 8: electronic component (package substrate) 9: BVH pad portion

Claims (4)

[Claims] 1. An electronic component, comprising: forming a solder precoat layer on a bonding pad portion for a mounting component having a BVH structure of a motherboard, depositing solder, and then mounting the electronic component on the motherboard. How to implement. 2. A solder precoat layer is formed on both a bonding pad portion for a mounting component having a BVH structure and a bonding pad portion for a mounting component having no BVH structure on a motherboard, and then the solder is deposited. A method for mounting an electronic component, wherein the electronic component is mounted on the electronic component. 3. A solder pre-coat layer is formed on both the mounting component bonding pad portion having the BVH structure of the motherboard and the mounting component bonding pad portion of the electronic component, and after the solder is deposited, the solder precoat layer is formed on the motherboard. A method for mounting an electronic component, comprising mounting the electronic component. 4. The method for mounting an electronic component according to claim 1, wherein a Ni / Au plating process is performed on the bonding pad portion for the mounted component in advance before forming the solder precoat layer. .