JPS5950555A - Method of producing sealed cap - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Technical Field] The present invention relates to packaging of integrated circuit chips, and more specifically to a method of manufacturing a cap for sealing a substrate on which an integrated circuit chip is mounted. It is.

Technology has now achieved miniaturization of electronic devices.

This miniaturization has been achieved by increasing the number of circuits that can be formed on an integrated circuit chip and by densely packaging integrated circuit chips into electronic devices.

FIG. 1 shows a prior art integrated circuit chip packaging module 10 used to package a plurality of chips 11. FIG. Chip 11 is mounted onto substrate 12 via solder balls 13 or other means. chip 1
Electrical connection to 1 is made via pin 14.

All chips 11 are hermetically sealed by caps 16, typically made of fired ceramic. The cap has a cavity 17 therein and is attached to the substrate 12 by a seal 19. Chip 11 is connected to cap 16 by thermal grease 18. Heat from the chip 13 is transferred to the cap via thermal conductive grease 18]
6 and the heat is radiated by the heat sink 21.

As chip packaging density increases, chip
The dimensional tolerances of packaging module 10 become tighter. For example, it is known to those skilled in the art that the thermal resistance of thermal grease 18 is directly proportional to its thickness. The thickness of thermal grease 18 must be precisely controlled to ensure the required degree of cooling of each integrated circuit chip J1.

Tight control of the distance between the tip and the cap (indicated by X in FIG. 1) is thus required. In order to accommodate the high density packaging required by future data processing devices, the distance between the chip and the cap must be controlled to within about 0.01 turns.

[Background technology]

Currently known technology does not allow mass production of caps with desired dimensional tolerances. For example, a ceramic cap with a desired cavity cannot be shaped in the green state and then fired. This is because the firing process distorts the cap. Similarly, cavities with the desired dimensions cannot be formed by grinding a fired ceramic plate. This is because rotary grinding with a polishing shaft is not compatible with rectangular cavities.

Caps can be manufactured with desired dimensional tolerances 1
One method is ultrasonic cutting. As is well known to those skilled in the art, in ultrasonic cutting, abrasive grains are placed in a liquid flowing between the workpiece and the ultrasonic cutting head. The cutting head vibrates with ultrasonic waves to drive the abrasive grains to produce a cutting action.

The shape of the cutting head determines the precision cutting pattern.

Cavities with desired dimensional tolerances may be created in the plate by ultrasonic cutting methods. Unfortunately, when ultrasonically cutting a flat cavity, the ultrasonic cutting head suffers from pitting (
It is known that the product becomes unusable after only 2 or 3 uses due to pitching and wear. Since the ultrasonic cutting head must be replaced every time two or three caps are made, ultrasonic cutting of flat cavities is not suitable for mass production of caps.

[Present invention]

The main objective of the present invention is to provide a new method of manufacturing a sealing cap for a substrate supporting a chip.

Another object of the present invention is to provide a method of manufacturing a ceramic cap with desired dimensional tolerances relative to conventional chip packaging modules.

Another object of the invention is to provide a method for mass producing sealing caps having desired dimensional tolerances.

The above and other objects are achieved in a method of making a cap by ultrasonically cutting a cavity in a plate having a plurality of pedestals at locations corresponding to the location of an integrated circuit chip on a substrate supporting the chip. More specifically, ultrasonic cutting of the cap is a two-step process. In a first step, a pattern of grooves is formed on the top surface of the plate. The groove pattern defines a plurality of pedestals at locations corresponding to integrated circuit-chip locations on the substrate. In a second step, each peak of the pedestal is ultrasonically cut to a critical distance from the top surface of the ceramic plate.

It has been found that the pedestal cap made by the method of the present invention maintains the desired dimensional tolerance between the chip and the pedestal top. Moreover, it has been found that the wear of ultrasonic cutting heads is dramatically reduced compared to the wear of cutting heads used in the manufacture of flat cavity caps. More specifically, cap 20 is used to replace worn out ultrasonic cutting heads for manufacturing pedestal camps.
It was also found that this is a significant improvement compared to every 2 to 3 caps in the flat hollow type cap. Thus, the cap manufacturing method of the present invention is suitable for mass production.

〔Example〕

In FIG. 1, a sealing cap 16 having a flat bottom cavity 17 is shown.
An integrated circuit chip packaging module 10 is shown including. Cap 16 is made by dry pressing and firing alumina (AQλOx) in a manner well known to those skilled in the art. Cap 16 may be made of other ceramics, such as glass, silicon nitride beryllium oxide, etc. Cap 16 is hermetically sealed onto substrate 12 by an encapsulant 19 of brass or other material. A plurality of chips 11 are attached to a substrate 12 by solder balls 13 or other electrical connection means. Chip IJ is thermally connected to cap 16 by thermal grease 18.

Pins 14 serve as electrical connectors to the module. The heat guided to the camp 16 is dissipated by the heat sink 21.

It has been found that the flat bottom cavities of ceramic camps made by conventional dry compaction and firing are slightly distorted. Although this distortion has not been much of a problem in the past, it will not be suitable for future high-density packaging applications.

More specifically, as mentioned above, future chip packaging will require chip-to-cap distances controlled to within 0.1 eave.

Figures 2-4 illustrate a method of manufacturing a ceramic cap that meets the dimensional tolerances described above.

FIG. 2 shows a dry pressed and fired ceramic plate 22 from which the ceramic cap of the present invention can be made. The surface of the ceramic plate 22 may be polished to remove distortion if desired.

FIG. 3 shows a first ultrasonic cutting step according to the invention. Ultrasonic cutting may be performed with any suitable ultrasonic cutting. In FIG. 3, a first cutting head 23, typically made of silicon carbide, is used to form a pattern of grooves 26 in the top surface of the ceramic plate 22. In FIG. The groove pattern defines a plurality of pedestals 24 in the ceramic plate 22. The pedestal 24 is provided at a location corresponding to the integrated circuit chip location on the substrate to which the ceramic cap will be attached.

The ultrasonic cutting head 23 wears out after cutting 200-300 caps. This is pitting
Contrast this with ultrasonic cutting heads for flat-bottom hollow-side cutting, which wear out after only cutting a few caps due to head corrosion. Premature wear is believed to be caused by eddy currents formed in the liquid flowing between the cutting head and the workpiece during ultrasonic vibration. The grooved configuration of the cutting head 23 eliminates these eddy currents, thus preventing premature head corrosion. When the cutting head 23 wears out (every 200 to 300 caps manufactured), it is not necessarily necessary to replace it, and it can be reused by scraping off the pitted surface.

In FIG. 4, the top of the pedestal 24 is ultrasonically cut by a second ultrasonic cutting head 27. Each pedestal may be cut a critical distance (indicated by y in FIG. 4) from a plane containing the top surface of ceramic plate 22.

Note that in FIG. 4 the pedestals 24 have all been cut to the same critical distance y. However, the pedestals 24 were different such that a different amount of thermal grease was placed between all the pedestals and their corresponding integrated circuit chips when the caps 22 were assembled into the chip packaging module. Those skilled in the art will understand that the critical distance may be cut. Non-uniform pedestal heights are desirable when all chips on the substrate consume different amounts of power or operate at different operating temperatures. Regardless of whether the cutting heights of the pedestals 24 are the same or different, when practicing the present invention, the critical distance is 0.0I.
It is preferable to control within n+m. Because the flat bottom cavity never cuts, premature cutting head wear due to eddy currents or other effects does not occur. Therefore, the cutting head is 2
It should also be noted that it only needs to be replaced or regenerated every time 00-300 heads are cut.

FIG. 5 shows a completed cap made in accordance with the present invention. Those skilled in the art will appreciate that the number, relative dimensions, and location of grooves 26 will be determined for the particular integrated circuit packaging module in which the cap is used. Cap 22 was typically made by dry pressing and firing alumina, but other ceramics such as glass, silicon nitride or beryllium oxide or other materials may be used.

FIG. 6 shows a cap 22 made in accordance with the present invention and incorporated into a chip packaging module 30. As shown in FIG. 6, a plurality of chips 31 are connected to solder balls 33
It is mounted on the board 32 by. A plurality of pins 34 are attached to the board 32. Cap 22 is sealed to base body 32 by brass sealant 39.

The camp 22 has a plurality of grooves 26 and a pedestal 24.

A predetermined amount of thermally conductive compound 38 is present between each pedestal 24 and the corresponding chip 31 . When the cap is made according to the invention, the critical distance l! between the pedestal 24 and the tip 31! 7
11X is precisely maintained.

Many variations on the above-described method of creating a camp are possible. For example, the dimensions of groove 26 are not as critical as the height of pedestal 24. Thus, the first ultrasonic cutting step described in FIG. 3 may be omitted if the ceramic plate 22 is originally molded or press-formed with the groove 26 and pedestal 24 of FIG. . For example, a dry pressed and fired ceramic plate having the shape shown in FIG. 3 may be provided. The pedestal 24 may then be ultrasonically cut to a critical distance as shown in FIG. 4 using only one ultrasonic cutting step.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of a prior art integrated circuit chip packaging module including a sealing cap with a flat bottom empty side; FIGS. 2-4 are diagrams illustrating a sealing cap manufacturing process according to the present invention; FIG. 5 shows a sealing cap made in accordance with the present invention, and FIG. 6 shows an integrated circuit chip packaging module including a ceramic cap made in accordance with the present invention. 22... Ceramic plate, 23... First ultrasonic cutting head, 24... Pedestal, 26... Groove, 27
...Second ultrasonic cutting head. Applicant International Business Machines
Corporation Sub-Agent Patent Attorney Shino 1) Yu Fumi FIG, 5 FIG, 6

Claims (1)

[Claims] A method for manufacturing a cap for sealing a substrate on which integrated circuit chips are mounted, the cap comprising a groove pattern on the top surface that defines a pedestal at a position corresponding to a plurality of integrated circuit chips on the substrate. A method for manufacturing a sealing cap comprising the steps of: forming a plate having a top surface of the pedestal; and ultrasonically cutting the top of the pedestal so as to be located at a predetermined distance below a plane containing the top surface of the pedestal.