Patent Application
20070114672
The present application claims priority from Japanese patent application No. 2005-333542 filed on Nov. 18, 2005, the content of which is hereby incorporated by reference into this application.
The present invention relates to a semiconductor device and its manufacturing technology, and particularly relates to an effective technology in the application to a thin semiconductor device like the system in package (SiP) which laminated a plurality of semiconductor chips on the wiring substrate.
The thin semiconductor device called a system in package (SiP) is provided with the package structure which mounted the microcomputer chip, the memory chip, etc. on the main surface of a wiring substrate, and sealed these semiconductor chips (it may only be hereafter called a chip) by resin.
The wiring substrate of the system in package includes the glass-epoxy-resin plate with which Cu (copper) wiring was formed in the main surface and the internal layer, for example, and a microcomputer chip and a memory chip are electrically connected to the above-mentioned Cu wiring via Au (gold) wire. The Cu wiring of the main surface of a wiring substrate is covered with the thin insulating film called solder resist in order to prevent contamination on the front surface of a wiring, and the short-circuit of wirings.
Many electrodes electrically connected to the above-mentioned Cu wiring are formed in the back surface of a wiring substrate, and the solder bump which forms the external connection terminal of a system in package is connected to each electrode. A system in package is mounted in the mother board of various electronic equipment etc. by doing reflow of the above-mentioned solder bump at the high temperature more than the melt temperature.
Japanese Unexamined Patent Publication No. 2002-93994 (Patent Reference 1) is related with the memory card which laminated a plurality of memory chips on the wiring substrate. This Patent Reference 1 points out the problem that the adhesive property of a chip and a wiring substrate falls, since irregularity of a wiring influences on the surface of solder resist and flatness falls when Cu wiring and solder resist are formed in the chip mounting region of a wiring substrate, when a chip is mounted in a wiring substrate using a paste agent. The technology which secures the flatness of a chip mounting region and strengthens adhesive property of a chip and a wiring substrate by not forming Cu wiring and solder resist in the chip mounting region of a wiring substrate is disclosed as the measures.
[Patent Reference 1] Japanese Unexamined Patent Publication No. 2002-93994
In order to mount a microcomputer chip and a memory chip on the wiring substrate of a system in package, where a dicing tape is stuck on the back surface of the semiconductor wafer (only henceforth a wafer) to which the preceding process (wafer process) completed, dicing is performed, and a wafer is divided into a plurality of chips. Next, one piece is peeled at a time from a dicing tape, and these chips are transported on a wiring substrate using the adsorption jig called an adsorption collet. The paste agent (adhesives) is beforehand applied to the chip mounting region of a wiring substrate using the paste coating equipment called a dispenser, and a chip is pasted up on the surface of a wiring substrate via this paste agent.
However, in recent years, in order to realize advanced features and a miniaturization collectively, as for the system in package, stacked package-ization which mounts a plurality of chips in three dimensions on a wiring substrate is advanced. When assembling such a stacked package, in order to suppress the increase in package thickness, it is required that thickness of a chip should be made thin to below 90□m, for example, about 50-60□m.
However, when thickness of a chip is made below 90□m, the problem that a paste agent will creep up from the end portion of a chip to the main surface side, and will cover the front surface of a bonding pad when pasting up a chip on the surface of a wiring substrate via a paste agent will occur. Since the paste agent has viscosity, the chip moves when pasting up a chip on the surface of a wiring substrate, and it is difficult to mount a chip on the surface of a wiring substrate in the state where it is stabilized. Since the thickness of a chip is as thin as below 90□m, the die strength of a chip may become low and a chip crack may be generated in a manufacturing process.
Then, in order to avoid such a problem, the adhesion material of the shape of a film called a die attach film (Die Attach Film) is used instead of a paste agent. Via this die attach film, a chip is pasted up on the surface of a wiring substrate, or pasting up other chips further on a chip is performed.
When using this die attach film, when sticking a dicing tape on the back surface of the wafer which the wafer process completed, the die attach film is first put between the wafer and the dicing tape. And after doing dicing of a wafer and the die attach film simultaneously in this state, the divided chip is peeled from a dicing tape with a die attach film. And after pasting up a chip on the surface of a wiring substrate via a die attach film, a die attach film is heated and adhesives are cured.
When the thickness of a wafer becomes thin, the strength will become weak, and when transporting to a dicing step, there is a possibility that a wafer may break. Therefore, the effect that the strength of a wafer is securable is also acquired by making a die attach film intervene between a wafer and a dicing tape.
However, the present inventor found out that the following problems would occur when assembling a stacked package and it is going to paste up a chip on the surface of a wiring substrate via a die attach film.
As mentioned above, in the stacked package which mounts a plurality of chips in three dimensions on a wiring substrate, it is required that thickness of respective chips should be made thin, for example to about 50-60□m. However, if the thick die attach film was used when pasting up the chip made thin on the surface of a wiring substrate or further laminating the other chip on a chip, since package thickness increases, it is required that thickness of the die attach film which is used should also be made thin according to the number of sheets of the chip to laminate.
However, since the level difference resulting from Cu wiring exists in the main surface of a wiring substrate, irregularity reflecting this level difference exists also on the surface of solder resist. When using the paste agent which is liquider than a die attach film, a paste agent will flow into the recess formed in the main surface of a wiring substrate. Therefore, compared with a die attach film, the flatness of the region which mounts the chip in the main surface of a wiring substrate is securable. On the other hand, since the viscosity of a die attach film is high compared with a paste agent when pasting up a chip on the surface of a wiring substrate and a thin die attach film is used, a cavity (void) occurs between a die attach film and solder resist. As a result, the so-called reflow crack that air and moisture in the above-mentioned cavity expand thermally, and destroys a package when doing reflow of the solder bump which is pasted on the back surface of the wiring substrate is caused.
A thick die attach film is stuck on the back surface of the chip of an undermost layer as the measures, and it is possible to apply pressure strong from the upper part when this chip is mounted on a wiring substrate. Since a die attach film will be embedded without a clearance in the clearance between solder resist and a chip when it does in this way, the generation of a cavity can be suppressed.
However, when a chip is mounted on a wiring substrate and strong pressure is applied on the surface of a chip, there is a possibility that the integrated circuit formed in the chip may receive a damage, or a chip may break. When the resin seal of the chip is done after laminating a plurality of chips, and electrically connecting wiring substrates and these chips with Au wire continuously on a wiring substrate as the measures, it is possible to embed a die attach film without a clearance in the clearance between solder resist and a chip using the heat of resin, and the welding pressure of a metallic mold.
However, by the above-mentioned method, when electrically connecting a chip with a wiring substrate with Au wire, the die attach film which intervenes between both is in un-hardening or a half-hardening state. Therefore, when doing bonding of the Au wire to the bonding pad of a chip, a chip moves slightly to a wiring substrate and the problem that the connection reliability of a bonding pad and Au wire falls occurs.
Thus, although the thin die attach film for example, less than 10□m can also be used between a lower layer chip and the upper chip since flattening of the main surface and back surface of a chip is done when laminating a chip on a wiring substrate using a die attach film, since a thick die attach film must be used between the chip of an undermost layer, and a wiring substrate, the height from the main surface of a wiring substrate to the chip of the top layer becomes large by that part, and the miniaturization of a system in package is hampered.
Since the die attach film made to intervene between chips and the die attach film made to intervene between a chip and a wiring substrate must be made into another specification, the assembling process of a system in package is complicated. As for the thick die attach film made to intervene between a chip and a wiring substrate, since a manufacturing cost is also high compared with a thin die attach film, the manufacturing cost of a system in package also becomes expensive.
A purpose of the present invention is to offer the technology of promoting the miniaturization of the semiconductor device which laminates a plurality of chips on a wiring substrate via a die attach film.
An other purpose of the present invention is to offer the technology which improves the reliability and the manufacturing yield of the semiconductor device which laminates a plurality of chips on a wiring substrate via a die attach film.
Other purposes of the present invention are to offer the technology of reducing the manufacturing cost of the semiconductor device which laminates a plurality of chips on a wiring substrate via a die attach film.
The above-described and the other purposes and novel features of the present invention will become apparent from the description herein and accompanying drawings.
Of the inventions disclosed in the present application, typical ones will next be summarized briefly.
As for a semiconductor device, a plurality of semiconductor chips are laminated via a die attach film over a main surface of a wiring substrate by which a plurality of wirings are formed in the main surface, and resin seal of the semiconductor chips is done, the semiconductor chip of an undermost layer is mounted via the die attach film among the semiconductor chips over a metal plate formed over the main surface of the wiring substrate, and a thickness of the die attach film which intervenes between the semiconductor chip of the undermost layer and the wiring substrate is a same as a thickness of a die attach film which intervenes between a lower layer semiconductor chip and an upper semiconductor chip.
A method of manufacturing a semiconductor device of this invention is a method of manufacturing a semiconductor device which does a resin seal of a plurality of semiconductor chips after laminating the semiconductor chips via a die attach film over a main surface of a wiring substrate by which a plurality of wirings were formed in the main surface, and comprises the steps of: (a) mounting a first semiconductor chip over the main surface of the wiring substrate via a first die attach film; and (b) mounting a second semiconductor chip over the first semiconductor chip via a second die attach film, wherein the first semiconductor chip is mounted via the first die attach film over a metal plate formed over the main surface of the wiring substrate.
Advantages achieved by some of the most typical aspects of the invention disclosed in the present application will be briefly -described below.
By laminating a plurality of chips via a die attach. film on the metal plate formed on the main surface of a wiring substrate, since the flatness of the main surface of a wiring substrate is securable, thickness of the die attach film which intervenes between the chip of an undermost layer and a wiring substrate can be made the same as the thickness of the die attach film which intervenes between a lower layer chip and the upper chip.
Hereafter, embodiments of the invention are explained in detail based on drawings. In all the drawings for describing the embodiments, members of a like function will be identified by like reference numerals and overlapping descriptions will be omitted.
The semiconductor device of this embodiment is the system in package (SiP) which piles up and mounts three chips (memory chips 19A and 19B and microcomputer chip 19C) on the main surface of wiring substrate 3, and which sealed these chips (memory chips 19A and 19B and microcomputer chip 19C) with mold resin 15.
Wiring substrate 3 is a multilayer interconnection substrate formed using general-purpose resin like glass epoxy resin as a core. Wiring (wiring pattern) 8 and metal plate (metal layer) 9 which etched and formed thin Cu (copper) foil of about 10□m-15□m in thickness are formed in the main surface. Ni (nickel) plating is performed to the front surface of Cu foil which forms wiring 8 and metal plate 9, and Au plating is further performed on Ni plated layer to a part of wiring 8 (the region where bonding of the Au (gold) wire is done, electrode). Metal plate 9 is functioning as a part of wiring 8, for example, a reference potential plate.
On metal plate 9, memory chip 19A is mounted via die attach film 11. Here, the bonding strength of die attach film 11 and Au plating is lower than the bonding strength of die attach film 11 and Ni plated layer. Therefore, as described above, only Ni plating is performed to the front surface of Cu foil which forms metal plate 9, and Au plating is not performed on Ni plated layer. On this memory chip 19A, second memory chip 19B is mounted via die attach film 11, and microcomputer chip 19C is mounted via die attach film 11 on second memory chip 19B. Metal plate 9 is formed in the flat region of one side of wiring substrate 3 in order to make flat the front surface (region in which a chip is mounted). That is, other conductor layers etc. are not formed between metal plate 9, and wiring substrate 3 of the lower part. The area of metal plate 9 is slightly larger than the area of memory chip 19A mounted on it. This is because the problem that a position drift of some occurred when a chip is mounted was taken into consideration. Solder resist (an insulating film, a protective film) 14 is formed in the circumference of metal plate 9, and height differs from the front surface of metal plate 9. That is, the height of the front surface of metal plate 9 and the front surface of solder resist 14 differs. Therefore, if the area of metal plate 9 and the area of memory chip 19A are formed in the same size, it is mounted so that a part of memory chip 19A may overlap in plan view with a part of solder resist 14 by the position drift at the time of mounting. Hereby, a cavity will occur between die attach film 11 and metal plate 9. However, in this embodiment, since the area of metal plate 9 is formed more greatly than the area of memory chip 19A to mount, it is possible to certainly mount in the region of metal plate 9.
All of die attach film 11 which intervenes between metal plate 9 and memory chip 19A of an undermost layer, die attach film 11 which intervenes between memory chip 19A and memory chip 19B, and die attach films 11 that intervene between memory chip 19B and microcomputer chip 19C include adhesion material of the same quality, and they have the same thickness (below 25□m, for example, about 5□m).
SRAM (Static Random Access Memory) is formed in the main surface of memory chip 19A of an undermost layer among the three above-mentioned chips (memory chips 19A and 19B and microcomputer chip 19C). The flash memory is formed in the main surface of memory chip 19B. The high-speed microprocessor (MPU: microprocessor unit) is formed in microcomputer chip 19C of the top layer.
As shown in
Bonding pad BP of memory chip 19A and wiring 8 (a part of wiring 8, an electrode) of wiring substrate 3 are electrically connected via Au wire 13. Bonding pad BP of memory chip 19B and wiring 8 of wiring substrate 3 are electrically connected via Au wire 13. Bonding pad BP of microcomputer chip 19C and wiring 8 of wiring substrate 3 are electrically connected via Au wire 13. That is, three chips (memory chips 19A and 19B and microcomputer chip 19C) are electrically connected to wiring substrate 3 by the wire-bonding system. A part of wiring 8 formed in one side of wiring substrate 3 is illustrated by
For example, internal wiring 24 of about four layers and the via hole which is not illustrated are formed in the inside of wiring substrate 3. 240 electrodes 25 electrically connected to wiring 8 via internal wiring 24 and a via hole are formed in the back surface of wiring substrate 3. As well as the wiring 8 and metal plate 9, internal wiring 24 and electrode 25 are formed by etching Cu foil, and Au plating is performed to the front surface of electrode 25 via Ni plating.
Solder bump 26 which forms the external connection terminal of a system in package (SiP) is connected to electrode 25 formed in the back surface of wiring substrate 3. A system in package (SiP) is mounted in the mother board of various electronic equipment etc. via these solder bumps 26. That is, wiring substrate 3 functions as a relay board (interposer) at the time of mounting the three above-mentioned chips (memory chips 19A and 19B and microcomputer chip 19C) in a mother board etc.
Solder resist 14 for preventing contamination of wiring 8 and the short-circuit of wiring 8 each other is formed in the main surface of wiring substrate 3. Solder resist 14 is an insulation film which includes polyimide resin etc. and whose thickness is 20 μm grade, and is formed throughout the main surface of wiring substrate 3 except for a part of wiring 8 (region where bonding of the Au wire 13 is done), and the front surface of metal plate 9. Similarly, solder resist 14 is formed in the back surface of wiring substrate 3 except for the front surface of electrode 25.
Thus, the system in package (SiP) of this embodiment has the BGA (Ball Grid Array) structure of 240 pins which laminated three chips (memory chips 19A and 19B and microcomputer chip 19C) on wiring substrate 3, and formed the system with these three chips.
The above-mentioned semiconductor manufacturing process includes a film formation step, the ion implantation step of an impurity, photolithography operation, an etching step, a metallizing step, a cleaning process, the test step between each step, etc. In the last process of this semiconductor manufacturing process, the good or bad of chip area 19A′ of wafer 1 is judged by the electrical test using a probe.
In order to manufacture a system in package (SiP), the second wafer with which the flash memory was formed and the third wafer with which the microcomputer was formed other than the above-mentioned wafer 1 with which SRAM was formed are prepared, but illustration is omitted about these wafers.
In order to manufacture a system in package (SiP), the thickness is made thin to below 90□m, for example about 50□m-60□m by polishing first the back surface of wafer 1 shown in the
Next, as shown in
Next, as shown in
Next, as shown in
Next, wafer ring 22 adhered on the periphery of dicing tape 21 is depressed below by descending expand ring 32 of pickup device 30. When it does in this way, dicing tape 21 will be extended in response to the strong tension which goes to a periphery from the central part without slackening horizontally.
Next, as shown in
Thus, memory chip 19A which peeled from dicing tape 21 with die attach film 11 is adsorbed and held at adsorption collet 34, and is transported by the next step (pellet attachment step). And when adsorption collet 34 which transported memory chip 19A to the next step returns to pickup device 30, according to the above-mentioned procedure, the following memory chip 19A will peel from dicing tape 21. Henceforth, according to the same procedure, memory chip 19A peels one piece at a time from dicing tape 21. Although illustration is omitted, by using the above-mentioned pickup device 30, it peels memory chip 19B from the second wafer with which the flash memory was formed, and peels microcomputer chip 19C from the third wafer with which the microcomputer was formed.
Memory chip 19A transported by the pellet attachment step is mounted on metal plate 9 of matrix substrate 20 via die attach film 11, as shown in
Next, after heat-treating matrix substrate 20 and doing complete cure of all the die attach films 11, as shown in
Then, by connecting solder bump 26 to electrode 25 of matrix substrate 20, and cutting mold resin 15 and matrix substrate 20 in a lattice manner along dicing line L shown in the
Thus, when three chips (memory chips 19A and 19B and microcomputer chip 19C) are laminated via die attach film 11 in this embodiment on wiring substrate 3, metal plate 9 is formed in the chip mounting region of wiring substrate 3, and memory chip 19A of an undermost layer is mounted on this metal plate 9. Since the flatness of the chip mounting region of wiring substrate 3 is securable by this, even if it makes thin thickness of die attach film 11 which intervenes between metal plate 9 and memory chip 19A of an undermost layer to below 10□m, for example, about 5□m, a cavity (void) does not occur in the lower layer of this die attach film 11.
Hereby, when doing reflow of the solder bump 26 which is pasted on the back surface of wiring substrate 3, the generation of a reflow crack can be suppressed and the reliability of a system in package (SiP) improves. Since die attach film 11 stuck on each back surface of three chips (memory chips 19A and 19B and microcomputer chip 19C) can be altogether made thin, the height from the main surface of wiring substrate 3 to microcomputer chip 19C of the top layer can be reduced, and the miniaturization of a system in package (SiP) can be promoted.
Since die attach film 11 stuck on each back surface of three chips (memory chips 19A and 19B and microcomputer chip 19C) is made to the same specification, the assembling process of a system in package (SiP) can be simplified. Since thickness of all the die attach films 11 can be made thin, the manufacturing cost of die attach film 11 can be lowered, and the manufacturing cost of a system in package (SiP) can be reduced.
Since memory chip 19A does not move to wiring substrate 3 at the time of wire bonding by doing the complete cure of all the die attach films 11 in advance of a wire-bonding step, the connection reliability of bonding pad BP and Au wire 13 improves.
By giving the function as a wiring which supplies reference potential (GND), for example to metal plate 9 formed in the chip mounting region of wiring substrate 3, the flexibility of a wiring design improves compared with the case where the metal plate which does not have a function as a wiring is formed in the chip mounting region of wiring substrate 3.
In the foregoing, the present invention accomplished by the present inventors is concretely explained based on above embodiments, but the present invention is not limited by the above embodiments, but variations and modifications may be made, of course, in various ways in the limit that does not deviate from the gist of the invention.
Although memory chip 19A was mounted in the embodiment on metal plate 9 formed in the chip mounting region of wiring substrate 3, For example, as shown in
This dummy chip 19D is a silicon chip obtained by doing dicing of the wafer which does not form an integrated circuit. Although the height from the main surface of wiring substrate 3 to microcomputer chip 19C of the top layer increases when dummy chip 19D is made to intervene between wiring substrate 3 and memory chip 19A, since it becomes possible to form wiring 8 also in the chip mounting region of wiring substrate 3, the flexibility of a wiring design improves.
When wiring 8 is formed in the chip mounting region of wiring substrate 3 and the front surface is covered with solder resist 14, irregularity occurs on the front surface of solder resist 14. Therefore, in order to prevent a cavity (void) occurring between dummy chip 19D and solder resist 14, by pasting up dummy chip 19D on solder resist 14 using die attach film 27 thicker than the die attach film 11, and applying strong pressure from the upper part, die attach film 27 is embedded without a clearance in the clearance between solder resist 14 and dummy chip 19D. In this case, since the integrated circuit is not formed in dummy chip 19D, it is convenient even if it applies pressure strong against the front surface.
Although the system in package which laminated three chips on the wiring substrate was exemplified in the embodiment, of course, the number of chips and the kind of chip which are laminated on a wiring substrate can be arbitrarily changed according to a system.
The present invention is effective technology applying to a thin semiconductor device like the system in package which laminated a plurality of chips on the wiring substrate.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2005-333542 | Nov 2005 | JP | national |
