JPH09134933A - Mounting structure of land grid array type of package - Google Patents

Abstract

PROBLEM TO BE SOLVED: To ease the stress caused by the difference of thermal expansion so as to improve reliability by providing a connection medium consisting of an organic material which has a conductive layer to connect the terminal electrode of a package with the electrode of a wiring board, on the surface. SOLUTION: This mounting structure is equipped with a land grid array type of package 1d which has a terminal electrode 2, a printed wiring board 6 which has an electrode 7 opposed to the terminal electrode 2, and a connection medium 5 which consists of organic material for electrically connecting the terminal electrode 2 of the package 1 with the electrode of the printed wiring board 6. The connection medium 5 eases the stress caused by the difference of thermal expansion, connecting the terminal electrode 2 with the electrode by, for example, solder 4. The connection medium 5 is spherical, and a conductor layer 3 is made on the surface. For the connection medium 5, the Young's modulus is 4GP or under, and the Young's modulus is lower than that of metal, so it is abundant in flexibility, and when the stress caused by the difference of thermal expansion between the package 1 and the printed wiring board 6 occurs, it is eased by the transformation of the connection medium 5.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a land grid array type package mounting structure.

[0002]

2. Description of the Related Art Recently, in order to miniaturize electronic devices and operate at high speed, semiconductor packages are connected in a grid pattern on the back side of packages such as BGA (ball grid array) and LGA (land grid array). There is a marked movement to use a package that does not have leads with electrodes.

This package has, for example, an LGA (Land Grid Array: Reference: Nikkei Electronics, August 2, 1993, p. 104, p. 104), in which a semiconductor chip 30 is mounted on a carrier substrate 31, as shown in FIG. ~
p. 118) type package 32, and the balls 3 made of solder are attached to the array-shaped terminal electrodes 36 of the package 32.
3 is mounted, and the package 32 is mounted via the solder balls 33 on the printed wiring board 35 having the same electrodes as the array-shaped terminal electrodes 34 (the semiconductor package is mounted on the printed wiring board and electrically connected. I was doing it.
By increasing the diameter of the solder ball 33, the package 32
Of the package 32 and the printed wiring board 35 by increasing the mounting height of the
It is a mechanism to reduce the dimensional difference between

[0004]

However, when such a package 32 is mounted on the printed wiring board 35 and soldered, stress generated due to a difference in thermal expansion between the printed wiring board 35 and the package 32 cannot be absorbed. , The problem of not getting reliable connection came out.

Hitherto, it has been a difficult technique to reliably connect opposing electrodes on two substrates having different thermal expansion coefficients. In most cases, the land grid array type package 32 and the printed wiring board 35 are made of different materials, so that they usually have different thermal expansion coefficients. For example, glass epoxy, which is often used for the printed wiring board 35, has a large thermal expansion coefficient of about 15 ppm / ° C. On the other hand, the land grid array type package 32 is made small to enclose a silicon chip (coefficient of thermal expansion of 3 ppm / ° C.), and when a glass ceramic substrate is used, the coefficient of thermal expansion is about 5 to 9 ppm / ° C. Therefore, if the size of the land grid array type package 32 becomes 30 mm square, a dimensional difference of 60 μm will occur between the terminal electrode 34 of the land grid array type package 32 and the electrode 36 of the printed wiring board 35 due to the temperature difference of 200 ° C. I will follow you. Therefore, when the terminal electrode 34 of the land grid array type package 32 and the electrode 36 of the printed wiring board 35 are firmly connected by soldering or the like, stress due to a difference in thermal expansion occurs due to a change in environmental temperature, and a weak place is broken. It leads to disconnection. On the other hand, by using the solder balls 33 in the mounting portion, the mounting height of the package 32 can be increased, and there is an advantage that the warp of the package 32 is alleviated by soldering. The package 32 is called a ball grid array because the solder balls 33 are mounted on the package 32. However, since the solder is a metal, the Young's modulus is about 6.
It is as high as 3 GPa, and when stress due to a difference in thermal expansion occurs due to a change in environmental temperature, the mounting portion or the solder ball 33
Stress is applied to the part, and it is destroyed in a weak place, leading to disconnection.

Therefore, an object of the present invention is to reduce the stress due to the difference in thermal expansion in the connection of the printed wiring board having the electrodes arranged in the same arrangement as the terminal electrodes of the land grid array type package having the terminal electrodes, thereby reducing the reliability. It is to provide a mounting structure of a certain land grid array type package.

[0007]

A land grid array type package mounting structure according to claim 1 is a land grid array type package having terminal electrodes, a printed wiring board having electrodes facing the terminal electrodes, and a package. And a connection medium made of an organic material having a conductor layer on its surface for electrically connecting the terminal electrode of (1) and the electrode of the printed wiring board.

According to the land grid array package mounting structure of the first aspect, since the connecting medium made of an organic material has a lower Young's modulus and is more flexible than a metal, the connecting medium is thermally expanded due to a change in environmental temperature. Even if a package with a different coefficient and a printed wiring board are electrically joined, it works to reduce the stress caused by the difference in thermal expansion,
It is possible to prevent disconnection and breakage of the joint that connects the package and the printed wiring board, and also to ensure the high reliability of the land grid array type package on the printed wiring board even in environmental tests such as heat cycle tests. , Effective when mounting a package having a large difference in thermal expansion coefficient from the printed wiring board.

A land grid array type package mounting structure according to a second aspect of the present invention is the mounting structure according to the first aspect, wherein the Young's modulus of the connecting medium made of an organic material is 4 GPa or less. According to the land grid array package mounting structure of the second aspect, the same effect as that of the first aspect can be obtained.

A land grid array type package mounting structure according to a third aspect of the present invention is the mounting structure according to the first aspect, wherein the connecting medium is spherical, cylindrical or prismatic. According to the land grid array type package mounting structure of the third aspect, in addition to the effect of the first aspect, it is possible to make the connection medium high to some extent, and in particular, it is possible to form the connection medium into a columnar shape, and It can be raised easily.

According to a fourth aspect of the present invention, there is provided a land grid array type package mounting structure according to the first aspect, wherein the connecting medium has a metal layer on its surface made of any one of Au, Al, Ag, Cu, Ni, Pb and Sn. Is to have.
According to the land grid array package mounting structure of the fourth aspect, the same effect as that of the first aspect can be obtained.

According to a fifth aspect of the mounting structure of the land grid array type package of the first aspect, the connection medium is a hollow spherical shape. According to the land grid array type package mounting structure of the fifth aspect, it is possible to further enhance the flexibility and to relieve stress more than the effect of the first aspect.

According to a sixth aspect of the present invention, there is provided a mounting structure of the land grid array type package according to the first aspect, wherein the terminal electrode of the land grid array type package and the connection medium are connected by either solder or a conductive adhesive. Is. According to the mounting structure of the land grid array type package of the sixth aspect, the same effect as the first aspect can be obtained.

In the mounting structure of the land grid array type package according to claim 7, in claim 6, the conductive component of the conductive adhesive is any one of Au, Al, Ag, Cu and Ni. According to the mounting structure of the land grid array type package of the seventh aspect, the same effect as the sixth aspect is obtained.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A land grid array type package mounting structure according to a first embodiment of the present invention will be described below with reference to FIGS. FIG. 1 is a sectional view of a mounting structure of a land grid array type package of the present invention. In FIG. 1, 1 is a land grid array type package, 2 is a terminal electrode, 3 is a conductor layer, 4 is solder, and 5 is a connection medium made of an organic material. Reference numeral 6 denotes a printed wiring board having electrodes arranged in the same arrangement as the array of terminal electrodes, and electrodes 7 are provided on the surface thereof. Reference numeral 8 is a conductor pattern, and 9 is solder. Note that FIG. 1 is a schematic diagram in which only a local portion is enlarged and illustrated for explaining the mounting structure of the land grid array type package of the present invention. Actually, the package 1 and the printed wiring board 6 have different sizes. Is normal.

That is, in this land grid array type package mounting structure, the land grid array type package 1 having the terminal electrodes 2, the printed wiring board 6 having the electrodes 7 facing the terminal electrodes 2, and the terminals of the package 1 are provided. A connection medium 5 made of an organic material for electrically connecting the electrode 2 and the electrode 7 of the printed wiring board 6 is provided.

Here, the land grid array type package 1 comprises a semiconductor chip 1a mounted on the surface of a carrier substrate 1b, and a terminal electrode 2 electrically connected to the semiconductor chip 1a penetrates through the carrier substrate 1b to pass through the carrier substrate 1b. It is provided on the back surface of 1b. The connection medium 5 connects the terminal electrode 2 and the electrode 7 with, for example, solder 4 as a connecting means. Then, it acts as follows to relieve the stress due to the difference in thermal expansion. First, the connecting medium 5 made of an organic material is spherical as shown in FIG. 2, and the conductor layer 3 is formed on the surface in advance. The conductor layer 3 is, for example, solder or the like. The solder paste 4 is printed on the terminal electrodes 2 on the surface of the package 1, and the connection medium 5 is arranged on each terminal electrode 2. After that, the solder is melted and connected in a reflow furnace. Thereby, the land grid array type package 1 having the connection medium 5
Is formed.

Next, a paste of solder 9 is printed on the electrodes 7 on the printed wiring board 6, and the package 1 is mounted so that the connection medium 5 made of an organic material and the electrodes 7 on the printed wiring board 6 correspond to each other. To do. Then, this mounting body is passed through a reflow furnace to melt and bond the solder 9. After passing through the reflow furnace, cooling begins, but the eutectic solder solidifies at about 180 ° C., and stress rapidly begins to accumulate in each part from this point. When the printed wiring board 6 is made of glass epoxy and the package 1 is made of glass ceramic, the printed wiring board 6 contracts from the package 1 and the terminal electrode 2 is pulled inward (toward the center of the package). if,
If there is no connecting medium 5 made of an organic material, the stress causes the package 1 and the printed wiring board 6 to be bent in a convex shape upward in the drawing. Temperature is -55 ° C for reliability test
Although a thermal shock test is performed, the connection is made in several tens of cycles with the combination of the package 1 using a glass ceramic substrate with a thickness of 1 mm and a size of 30 mm square and the printed wiring board 6 made of a glass epoxy with a thickness of 1.6 mm. Destroy. When the connection medium 5 made of an organic material is present, the stress at the time of temperature decrease serves as an absorbing role like an insulating flexible sheet, and a large amount of stress cannot be accumulated. That is, the connection medium 5 made of an organic material has a Young's modulus of 4 GPa or less, and has a Young's modulus lower than that of a metal, and thus is highly flexible. Therefore, when a stress due to a difference in thermal expansion occurs between the package 1 and the printed wiring board 6 due to a change in environmental temperature, it is possible to eliminate the stress by deforming the connection medium 5 made of an organic material. The same applies when the thermal expansion coefficient of the package 1 is larger than that of the printed wiring board 6.

It can be said that a material having heat resistance such as polyimide or silicone is suitable as a material of the connecting medium 5 made of an organic material because it is hardly changed by heat treatment such as solder reflow. However, even a material having a low heat resistance temperature can be used as long as the material is not completely liquefied or carbonized during solder reflow. The coefficient of thermal expansion is preferably close to the coefficient of thermal expansion of the conductor layer 3 formed on the surface of the connecting medium 5 made of an organic material.

In this embodiment, an example of a connecting medium 5 made of an organic material, in which a polyimide having a Young's modulus of 3.3 GPa is used as a main material and a conductive layer 3 made of solder is formed on a surface of a metal layer made of nickel, is formed. I will list them below. That is,
A metal layer of nickel having a thickness of 5 microns was formed on a main material having a diameter of polyimide of 500 microns, and a conductive layer 3 was formed thereon by solder plating having a thickness of 15 microns. The diameter after formation of the conductor layer 3 was 540 microns. Next, a solder paste (OZ-63-201C-50-9, manufactured by Senju Metal Co., Ltd.) was used as a metal plate on the terminal electrodes 2 of the land grid array type package 1 having a ceramic substrate as a carrier substrate. Then, the connection medium 5 made of an organic material was mounted on the terminal electrode 2 and passed through a reflow furnace to melt-bond the solder 4. A solder paste similar to eutectic solder is printed on the electrodes 7 of the printed wiring board 6 by a metal plate, the package 1 on which the connection medium 5 made of an organic material has been mounted is mounted on the printed wiring board 6, and passed through a reflow furnace. The solder 9 was melt-bonded. A reliability test was performed on the mounted body by a heat cycle test of −40 degrees (30 minutes) to 100 degrees (30 minutes) shown in JIS C0025.
In the mounting of the printed wiring board of the land grid array using the solder balls of the micron diameter (Young's modulus of 6.3 GPa), the open occurred at 200 cycles, but in this example, it was 600 cycles, which was significantly reliable. The property has improved.

A second embodiment of the present invention is shown in FIGS. 3 and 4. That is, in this land grid array type package mounting structure, in the first embodiment, the connection medium 14 made of an organic material has a cylindrical shape as shown in FIG. As an example, a metal layer of nickel of 5 microns is formed on a cylindrical column of silicone having a cylindrical height of 800 microns and a diameter of 500 microns and a Young's modulus of 0.02 GPa. The layer 3 is formed by plating. Solder paste (OZ-63-2 manufactured by Senju Metal Co., Ltd.) on the terminal electrode 2 of the package 1 having a ceramic substrate as a carrier substrate.
01C-50-9) is printed using a metal plate, and the connecting medium 5 made of an organic material is oriented in the connecting direction of the package 1 and the printed wiring board 6 so that the circular portion is on the terminal electrode 2 side. To this end, the connection medium 5 was mounted on the terminal electrode 2 and passed through a reflow furnace to melt-bond the solder 4. A solder paste similar to eutectic solder is printed on the electrodes 7 of the printed wiring board 6 by a metal plate, the package 1 on which the connection medium 5 made of an organic material is mounted is mounted, and the solder 9 is melted by passing through a reflow furnace. Joined. This mounting body is JIS standard C
A reliability test was conducted by a heat cycle test of -40 degrees (30 minutes) to 100 degrees (30 minutes) shown by 0025. As a result, a land grid array printed wiring board using solder balls having a diameter of 500 microns was obtained. Implementation of 20
In contrast to the case where the open occurs in 0 cycle, the reliability is greatly improved to 1000 cycles in this embodiment.

Further, since the connecting medium 5 has a cylindrical shape, it has the following advantages. That is, it is generally known that the mounting height of the package 1 on the printed wiring board 6 is increased to reduce the stress caused by the difference in thermal expansion due to the change in the environmental temperature. Although it is possible to increase the height to some extent by using the spherical body as in the first embodiment, the diameter of the sphere must be increased in order to make the height higher. However, in that case, the connection medium 5 may be connected to the adjacent connection medium 5. Therefore, in order to increase the height of the connection medium 5, it is necessary to change the spherical body into a columnar shape. Further, in a ball grid array using solder balls as a connection medium, it is difficult to form columnar objects because the material is solder. However, the connection medium 5 made of an organic material can have any shape.

The connection medium 5 may have a prismatic shape as shown in FIG. 5 instead of the columnar shape, and other columnar shapes are also included in the present invention. A third embodiment of the present invention is shown in FIG. That is, the mounting structure of this land grid array type package has a spherical shape as shown in FIG. 2B instead of the connecting medium 5 made of the spherical organic material of the first embodiment shown in FIG. The connection medium 5 has a spherical hollow 11 formed concentrically at the center of the above. By making the spherical body hollow, the connection medium 5 having higher flexibility can be formed. As an example, a polyurethane having a Young's modulus of 0.6 GPa is used as a main component, and a spherical diameter is 70
A conductive layer 3 made of Cu was formed to a thickness of 20 μm on a connecting medium 5 made of an organic material having a diameter of 0 μm and a diameter of the hollow 11 of 400 μm. Solder paste (OZ-63-201C-50-9, manufactured by Senju Metal Co., Ltd.) is printed on the terminal electrodes 2 of the land grid array type package 1 having a ceramic substrate as a carrier substrate using a metal plate. A connection medium 5 made of an organic material was mounted on each terminal electrode 2 and passed through a reflow furnace to melt-bond the solder 4. A solder paste similar to eutectic solder is printed on the electrodes 7 of the printed wiring board 6 by a metal plate, the package 1 on which the connection medium 5 made of an organic material is mounted is mounted, and the solder 9 is melted by passing through a reflow furnace. Joined. This mounting body is J
-40 degrees (30 minutes) shown in IS standard C0025
When a reliability test was conducted by a heat cycle test of -100 degrees (30 minutes), an open occurred at 200 cycles in the mounting of a land grid array printed wiring board using a solder ball having a diameter of 500 microns. On the other hand, in this embodiment, the reliability is greatly improved to 800 cycles.

Although a carrier substrate made of ceramic as a base material has been taken as an example of the land grid array type package 1, the same effect can be obtained with a carrier substrate made of an organic material and its package. A fourth embodiment of the present invention will be described with reference to FIG. That is, in the mounting structure of the land grid array type package of the first to third embodiments, the terminal electrodes 2 of the land grid array type package 1 and the connection medium 5 made of an organic material are solder paste. Connected,
For devices in which Pb cannot be used, a conductive adhesive containing no Pb is effective.

Therefore, in the fourth embodiment, a conductive adhesive (for example, product number 181 paste manufactured by Techno Alpha Co., Ltd.) is used in place of the solder 4 and 9 as the connecting means (not shown). This conductive adhesive uses Ag as a conductor. A conductive adhesive is applied on the terminal electrodes 2 of the land grid array type package 1 by a screen printing method or the like. A connection medium 5 made of an organic material on which a conductive layer 3 of Ag having a thickness of 15 μm is formed by a plating method is arranged on the printed terminal electrodes 2, and the conductive adhesive is cured at a predetermined temperature. Next, a conductive adhesive is printed on the electrodes 7 of the printed wiring board 6 by a screen printing method to mount a package mounted with a connecting medium made of an organic material, and cured at a predetermined temperature.

In this way, the land grid array type package 1 is mounted on the printed circuit board 6. This mounting body was subjected to a reliability test by a heat cycle test of −40 degrees (30 minutes) to 100 degrees (30 minutes) shown in JIS standard C0025. As a result, a land using a solder ball with a diameter of 500 μm was used. In the mounting of the printed wiring board of the grid array, an open occurred in 200 cycles, whereas in the fourth embodiment, an open occurred.
The reliability was greatly improved to 0 cycle.

In the fourth embodiment, a conductive adhesive containing Ag as a conductor is used, but Au, Cu,
The same effect can be obtained with a conductive adhesive containing Al or Ni as a conductor. However, it is not limited to these. The metal layer of the connection conductor made of an organic material is Au,
It may be any of Al, Ag, Cu, Ni, Pb and Sn, but is not limited thereto.

[0028]

According to the mounting structure of the land grid array type package according to the first aspect of the invention, since the connecting medium made of an organic material has a lower Young's modulus and is more flexible than a metal, the connecting medium has a high flexibility. Even if a package with a different thermal expansion coefficient and a printed wiring board are electrically joined, it works to relieve the stress caused by the difference in thermal expansion, and breaks or breaks in the joint that connects the package and the printed wiring board. It is possible to prevent the above, and also to ensure the high reliability of the land grid array type package on the printed wiring board even in environmental tests such as heat cycle tests, and to mount the package with a large difference in thermal expansion coefficient from the printed wiring board. It becomes effective when you do.

According to the land grid array type package mounting structure of the second aspect, since the Young's modulus of the connecting medium made of the organic material is set to 4 GPa or less in the first aspect, the same effect as the first aspect is obtained. According to the land grid array type package mounting structure of the third aspect, in the first aspect, the connecting medium is any one of spherical, columnar and prismatic. Therefore, in addition to the effect of the first aspect, the connecting medium can be made high to some extent. In particular, it is possible to form a columnar shape with an organic material, and it is possible to easily increase the height of the connection medium.

According to the mounting structure of the land grid array type package of the fourth aspect, in the first aspect, the connecting medium is Au, Al, Ag, Cu, Ni, P on the surface thereof.
Since it has a metal layer made of either b or Sn,
This has the same effect as the first aspect. According to the land grid array type package mounting structure of the fifth aspect, in the first aspect, since the connection medium is a hollow spherical shape, the flexibility is further enhanced and the stress is relieved more than the effect of the first aspect. It becomes possible.

According to the mounting structure of the land grid array type package according to claim 6, in claim 1, the terminal electrode of the land grid array type package and the connection medium are connected by either solder or a conductive adhesive. Therefore, the same effect as claim 1 is obtained. The land grid array type package mounting structure according to claim 7 is the structure according to claim 6, wherein the conductive components of the conductive adhesive are Au, Al, Ag, and Cu.
Since either Ni or Ni is used, the same effect as claim 6 is obtained.

[Brief description of the drawings]

FIG. 1 is a sectional view of a mounting structure of a land grid array type package according to a first embodiment of the present invention.

FIG. 2 is a perspective view of a spherical connecting medium.

FIG. 3 is a sectional view of a mounting structure of a land grid array type package according to a second embodiment.

FIG. 4 is a perspective view of a columnar connection medium.

FIG. 5 is a perspective view of a prismatic connection medium.

FIG. 6 is a perspective view of a hollow spherical connecting medium according to a third embodiment.

FIG. 7 is a cross-sectional view of a ball grid array using a conventional solder ball.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Land grid type package 2 Terminal electrode 3 Conductor layer 4 Solder which is a connecting means 5 Connection medium made of an organic material 6 Printed wiring board 7 Electrode 8 Conductor pattern 9 Solder which is a connecting means 11 Hollow

Claims (7)

[Claims] 1. A land grid array type package having terminal electrodes, a printed wiring board having electrodes facing the terminal electrodes, the terminal electrodes of the package and the electrodes of the printed wiring board are electrically connected to each other. A land grid array package mounting structure comprising a connecting medium made of an organic material having a conductor layer for connection on its surface. 2. The land grid array package mounting structure according to claim 1, wherein the Young's modulus of the connecting medium made of an organic material is 4 GPa or less. 3. The mounting structure of a land grid array type package according to claim 1, wherein the connection medium is one of spherical, columnar and prismatic. 4. The connecting medium has Au, Al, A on its surface.
The land grid array package mounting structure according to claim 1, further comprising a metal layer made of any one of g, Cu, Ni, Pb, and Sn. 5. The connecting medium has a hollow spherical shape.
Mounting structure of the described land grid array type package. 6. The mounting structure of a land grid array type package according to claim 1, wherein the terminal electrode of the land grid array type package and the connection medium are connected by either solder or a conductive adhesive. 7. The conductive component of the conductive adhesive is Au, Al, A
7. The land grid array package mounting structure according to claim 6, wherein the mounting structure is any one of g, Cu and Ni.