JP2001024094A - Array package and printed wiring board and electronic equipment on which array package is mounted - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent occurrence of cracks in connections by improving connection reliability between a substrate and a printed wiring board in a semiconductor package having a substrate on which terminals are formed in an array. SOLUTION: This array package has a substrate 1 on which a semiconductor chip is mounted and terminals 2, 3, 4 are arranged in an array. The outline of the substrate 1 is formed in a polygonal shape having not less than six corners or in a generally circular shape. Since the outermost row of terminals is positioned along the outline of the substrate, the terminals are arranged generally in the same distance from the center of the substrate. Furthermore, to enhance connection between the substrate and the printed wiring board, terminals not electrically connected can be provided in the outer periphery of the substrate, where the terminals are not arranged.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a structure of an array type multi-terminal LSI package exhibiting high connection reliability against thermal stress. The present invention also relates to a structure of a highly reliable printed wiring board unit on which the array type package of the present invention is mounted, and a structure of an electronic device equipped with the printed wiring board unit.

[0002]

2. Description of the Related Art In recent years, as electronic devices have become more sophisticated, semiconductor devices have become more highly integrated and the number of external terminals has increased, and BGAs (balls) having more than 500 connection terminals have been formed.
GridArray) packages are also appearing. BGA
In the type package, a substantially spherical terminal such as a solder bump is formed on the lower surface of a substantially square package substrate, and is mounted and connected to a land on a printed wiring board to form an electric conduction path. In addition, electronic devices have been miniaturized, and packages have also been miniaturized. In response to this trend, devices having terminals with even smaller intervals have been developed.

FIG. 6 is a back view of a BGA package substrate showing a conventional example. Reference numeral 12 denotes a substrate of a small package having relatively small pins, 2 denotes a solder ball formed on a signal electrode, 3 denotes a solder ball formed on a ground electrode, 4
Is a solder ball formed on the power supply electrode. A semiconductor is mounted on the surface of the substrate. Then, the package is printed with cream solder on the printed wiring board, mounted on the printed wiring board in a normal reflow process, and the printed wiring board unit on which the electronic components are mounted is incorporated in an electronic device.

[0004]

However, as the number of pins increases in the grid array package and the pitch becomes narrower, the following problem has arisen. In the grid array package having a relatively wide pin interval, the number of pins increases. The package size is getting bigger and bigger. Usually, the substrate for the package is made of a substrate made of a composite material of ceramic or high heat-resistant resin and glass fiber. On the other hand, since the printed wiring board on which the grid array package is mounted uses an inexpensive glass epoxy substrate, the two have different coefficients of thermal expansion. Since the thermal expansion coefficient of the substrate of the grid array package is small and the thermal expansion coefficient of the printed wiring board is large, the connection portion is subjected to heat stress due to heating and cooling processes during mounting and heat generation of the semiconductor during use and the use environment. . In particular, the terminals located at the corners of the square package substrate are subjected to the maximum stress, so that the connection portion is easily cracked or disconnected. This tendency naturally becomes a problem as the package size increases. As described above, the problems of cracks and disconnections lead to a decrease in the reliability of the printed wiring board unit and thus of the electronic device.

[0005] In addition, as the frequency of signals increases, the square package causes the following problems.
In other words, although the wiring pattern is short at the terminal almost at the center of the square package, the wiring pattern in the package substrate becomes long up to the terminal located at the corner of the package, so that the inductance becomes large and high-frequency transmission becomes disadvantageous. Therefore, it is necessary to use a terminal arranged at substantially the center of the package as a terminal for transmitting a signal of a higher frequency, which is a design limitation.

In electronic devices such as mobile phones and digital cameras that need to be reduced in size and weight, there is a strong demand for downsizing of packages, and accordingly, the distance between terminals is reduced, and the diameter of solder bumps and the like is reduced. It is getting smaller rapidly. And, as the diameter of the solder bumps becomes smaller, the connection strength per terminal also becomes weaker, and the problem of thermal stress due to the difference between the thermal expansion coefficient of the grid array package and the printed wiring board on which the grid array package is mounted as described above is more pronounced. growing.

As a method of suppressing the stress due to the difference in the coefficient of thermal expansion between the grid array package and the printed wiring board on which the grid array package is mounted, for example, a method as disclosed in Japanese Patent Application Laid-Open No. H10-022341 has been proposed. That is, in the BGA package, a convex portion is formed on a rear surface of a substrate on which a semiconductor chip is mounted, in a region close to the center of the rear surface, a concave portion is formed around the convex portion, and solder is formed on the convex portion. A method of arranging a small ball, arranging a large solder ball in a concave portion to assemble a BGA package, and mounting the BGA package on a mother board has been proposed.

However, in such a method, the BGA
The cost increases due to the formation of irregularities on the package substrate, and the use of large-sized solder balls on the outer periphery requires the use of large electrodes. There is.

In view of the above problems, the present invention relates to a package structure for improving connection reliability even when there is a difference in thermal expansion coefficient between an array package substrate and a printed wiring board. An object of the present invention is to provide a structure of a printed wiring board unit and an electronic device with higher reliability. Another object of the present invention is to provide an LSI package suitable for high-speed transmission in a higher frequency environment.

[0010]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides an LSI package for surface mounting in which terminals are formed in an array. The array package is formed in a shape or a substantially circular shape, and has a structure in which the outermost rows of terminals are arranged along the outer shape to uniformly distribute stress. Further, in a quadrangular surface mounting LSI package in which terminals are formed in an array, the outermost rows of terminals are arranged in a polygonal shape of hexagons or more, or in a substantially circular shape so that stress is uniformly dispersed. You can also.

In a square-shaped surface mounting LSI package in which terminals are formed in an array, the outermost rows of terminals formed by signal terminals, power supply terminals, and ground terminals are formed in a polygonal shape having a hexagonal shape or a substantially circular shape. An array package in which terminals are arranged so as to have a shape and terminals that are not electrically connected to other areas are arranged can be formed.

Further, the BGA package in which the connection terminals of the respective terminals are formed in a ball shape may be used, or only the electrodes having no solder balls and plated with gold or solder may be used. In that case, cream solder is printed on the printed wiring board, and the electrodes of the package and the electrodes of the printed wiring board are directly soldered by reflow. Further, the reliability of the printed wiring board unit and the electronic device can be further improved by using the above array package.

[0013]

Next, an embodiment of an array package according to the present invention will be described with reference to the drawings. FIG. 1 is a back view of a BGA package showing a first embodiment of the present invention. In this embodiment, the package substrate 1 is formed in an octagonal shape, and on its back surface, a solder ball 2 as a connection terminal formed on a signal electrode, and a solder ball formed on a ground electrode. 3, and a solder ball 4 formed on the power supply electrode. Then, a semiconductor is mounted on the surface of the substrate 1. Solder ball 2,
Reference numerals 3 and 4 are arranged in a lattice pattern on the back surface of the package, and the outermost solder balls are arranged along the inside of the outer peripheral edge of the octagonal substrate so that the distances from the center of the substrate are substantially equal.

The package thus formed is mounted on a printed circuit board in a normal reflow step via these solder balls, and a printed wiring board unit on which electronic components are mounted is incorporated in an electronic device. Therefore, thermal stress due to the difference in thermal expansion coefficient between the package and the printed wiring board is applied to the solder balls forming the connection between them, and the maximum stress is applied to the outermost solder balls. Since the stresses are at substantially equal distances from each other, the stress is distributed to the respective solder balls and equalized, so that cracks in the connection portions do not occur.

Next, a second embodiment of the present invention will be described. FIG. 2 is a rear view of a BGA package showing a second embodiment of the present invention. The package substrate 5 is formed in a circular shape, and the solder balls 2, 3, and 4 are arranged in a grid pattern on the back surface of the substrate 5, and the outermost solder balls extend substantially along the inside of the circular periphery of the substrate 5. The distance from the center of the substrate 5 is substantially equal.

In the third embodiment, as shown in FIG. 3, solder balls 2, 3, and 4 are formed on the back surface of a rectangular substrate 6. In this embodiment, the outer shape of the substrate is square, but the solder balls are arranged in a grid so that the outermost solder balls form an octagon as in the first embodiment. Therefore, the outermost solder balls are disposed at substantially the same distance from the center of the substrate regardless of the outer shape of the substrate, and have an effect of equalizing thermal stress.

Next, a fourth embodiment will be described with reference to FIG. The substrate 6 has a rectangular outer shape, and FIG. 4 is a rear view thereof. On this back surface, a signal electrode 8, a ground electrode 9, and a power supply electrode 10 are arranged such that the outermost electrodes form an octagon. Therefore, the outermost electrodes are arranged at substantially the same distance from the center of the substrate 6. At each corner of the substrate, an independent, large land 7 that is not electrically connected to the substrate is provided. By providing the land 7, the thermal stress generated between the substrate and the wiring board can be concentrated on the land 7 and the stress can be dispersed. Although this package does not have solder balls as connection terminals formed in advance, cream solder can be printed on a printed wiring board and can be mounted on the printed wiring board in a normal reflow process. Further, the printed wiring board unit on which the electronic components are mounted is incorporated in an electronic device.

FIG. 5 is a back view of the package showing the fifth embodiment. The board 6 has a quadrangular outer shape, and is electrically connected to each corner of the solder balls 2, 3, and 4 arranged in a grid in order to increase the bonding strength between the board 6 and the wiring board. Solder balls 11 for bonding, which are provided on independent lands that are not provided, are arranged to enhance the bonding strength.
In this manner, an independent land that is not electrically connected for intentionally concentrating stress is provided in the square of the substrate, and the solder ball 11 of this land is provided so that the outermost periphery of the outer periphery where electrical conduction is obtained is provided. The terminals have a structure in which the distance from the center of the octagonal substrate is substantially equal and stress is distributed to each terminal. In this package, cream solder is printed on a printed wiring board, mounted on the printed wiring board in a normal reflow process, and a printed wiring board unit on which electronic components are mounted is incorporated in an electronic device.

[0019]

According to the present invention, in a surface mounting LSI package in which terminals are formed in an array, the outer shape of a substrate on which terminals are formed is formed into a polygonal shape of hexagons or more, or a substantially circular shape. By arranging the outermost rows of terminals along the shape, the stress can be dispersed uniformly, so that the connection reliability due to thermal stress can be greatly improved. In addition, since the distance between the terminals from the center of the substrate is substantially equal in a radial manner, there is no restriction on the design of the arrangement for transmitting high-frequency signals.

Further, regardless of the outer shape of the surface mounting LSI package in which the terminals are formed in an array, the outermost rows of the terminals are arranged in a hexagonal or larger polygonal shape or a substantially circular shape to distribute the stress uniformly. The same effect as described above can be obtained by adopting the structure.

Furthermore, the terminals are arranged so that the external shape formed by the signal terminal, the power supply terminal, and the ground terminal is a polygonal shape of six or more hexagons or a substantially circular shape, and is electrically connected to other areas by electrically independent bonding. The connection reliability can be further improved by adopting a structure in which terminals are arranged.

[Brief description of the drawings]

FIG. 1 is a rear view showing a first embodiment of a substrate of an array package according to the present invention.

FIG. 2 is a back view showing the second embodiment.

FIG. 3 is a rear view showing the third embodiment.

FIG. 4 is a rear view showing a fourth embodiment.

FIG. 5 is a back view showing the fifth embodiment.

FIG. 6 is a back view showing a conventional array package.

[Explanation of symbols]

 1, 5, 6, 12 Array package substrate 2 Signal electrode solder ball 3 Ground electrode solder ball 4 Power supply electrode solder ball 7 Land not electrically connected 8 Signal Electrode 9 Electrode for ground 10 Electrode for power supply 11 Solder ball not electrically connected

Claims (8)

[Claims] 1. An LSI package for surface mounting in which terminals are formed in an array, wherein an outer shape of a substrate on which the terminals are formed is a polygonal shape having a hexagonal shape or more, or an approximately circular shape. package. 2. The array package according to claim 1, wherein the outermost rows of the terminals formed in an array are arranged along the outer shape of the substrate having a hexagonal or more polygonal shape or a substantially circular shape. 3. An SLI package for surface mounting in which terminals are formed in an array, wherein the outer shape of the substrate on which the terminals are formed is a quadrilateral, and the outermost row of the terminals is a polygonal shape of hexagons or more. Alternatively, an array package characterized by being arranged in a substantially circular shape. 4. The array package according to claim 3, wherein a terminal that is not electrically connected is disposed on a portion of the substrate, on the outermost row of the terminal, where the terminal is not disposed. 5. The array package according to claim 1, wherein connection terminals are formed on each terminal. 6. The array package according to claim 5, wherein the connection terminals are formed in a ball shape. 7. A printed wiring board unit on which the array package according to claim 1 is mounted. 8. An electronic device equipped with the printed wiring board unit according to claim 7.