JPS6159660B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an IC module suitable for configuring, for example, a high-speed logic circuit equipped with a bipolar integrated circuit (IC) that operates with a large current, and in particular, the present invention relates to an IC module that is suitable for configuring a high-speed logic circuit etc. equipped with a bipolar integrated circuit (IC) that operates with a large current. By arranging them side by side on the wiring board by bonding and thermally bonding a heat sink to the back side of each integrated circuit device,
This makes it possible to improve both the packaging density and the heat dissipation effect.

Conventionally, IC modules that take heat dissipation from IC chips into consideration have been made by die-bonding multiple bipolar LSI chips onto a thick-film multilayer wiring board made of alumina ceramics, and by using tape carrier technology to wire the electrodes on each LSI chip onto the wiring board. A structure was proposed in which the heat of each LSI chip was dissipated through the wiring board by appropriately connecting the layers (for example, Nikkei Electronics Magazine, 1977
(See April 18, 2015, pp. 100-119).

However, this type of IC module has the drawback that the wiring board has a thick film multilayer wiring structure, and therefore the packaging density cannot be increased very much. In order to increase the packaging density, it is possible to adopt a thin film multilayer wiring structure that incorporates a vapor deposition or etching process.
Since a material with poor thermal conductivity such as SiO ₂ or Al ₂ O ₃ is used, there is a disadvantage that, together with the fact that the substrate material is alumina ceramics, sufficient heat dissipation from each IC chip cannot be expected.

Therefore, an object of the present invention is to provide a novel IC module that can both improve packaging density and promote heat dissipation.

The IC module according to the present invention is characterized in that one main surface of the heat sink is thermally coupled to the back side of the integrated circuit device bonded to the wiring board via flexible leads, Hereinafter, embodiments shown in the accompanying drawings will be described in detail.

FIG. 1 shows an IC module according to an embodiment of the present invention, in which 1 is a plurality of Si IC chips including a high-speed logic bipolar LSI that operates with a large current, 2 is alumina ceramics, and each
A multilayer wiring board 3 has a heat radiation fin 3A, and a heat sink made of Al is fixed to the back surface of each IC chip 1 via a brazing material. 4 represents a wiring board 2 and A flange 5 has one end for fixing the heat sinks 3 to each other and sealing the IC chip 1 in the space between the substrate 2 and the heat sink 3.
flexible leads whose other ends are bonded to electrodes on the IC chip 1 and to wiring layers on the wiring board 2;
6 is a terminal pin provided to lead out the terminal portion of the wiring layer arranged on one main surface of the wiring board 2 to the opposite main surface; 7 is a bolt for fixing the heat sink 3 to the flange 4. .

Before the heat sink 3 and the wiring board 2 are fixed to each other, each IC chip 1 has a flexible lead 5.
The flexible lead 5 is located at the position indicated by the two-dot chain line in the figure, corresponding to the extending position of Therefore, it comes to the position shown by the solid line, which is closer to the wiring board 2 than the position of the two-dot chain line, and is fixed to the heat radiator 3 in such a way that it is pressed against the heat radiator 3 by the spring back pressure of the flexible lead 5. be. For this reason, the back of each IC chip 1 is connected to the heat sink 3.
It becomes tightly thermally coupled to one side of the surface, resulting in a good heat dissipation effect. At this time, even if the heat sink, brazing material, IC chip, etc. expand thermally due to the heat generated during operation of the IC chip, the flexible leads absorb the excess thermal stress. It is possible to reduce the occurrence of cracks in the chip, and also to prevent the occurrence of electrical connection defects between the wiring board and the IC chip. Moreover, each IC chip 1 and the heat sink 3 can be placed in a state of mere pressurized contact, and in such a case, heat generated due to the difference in coefficient of thermal expansion, as in the case where they are fixed with a brazing filler metal etc. Situations such as clicks in the IC chip 1 due to stress are less likely to occur, and good results can be obtained in terms of reliability. In addition, heat is radiated from the back side of each IC chip 1 to connect each IC chip 1 to the wiring board 2.
Since the wiring board 2 does not need to be in close contact with the wiring board 2, it is now possible to use not only a thick film multilayer wiring structure but also a thin film multilayer wiring structure, making it possible to significantly improve packaging density. Become.

Next, details of each component of the above-mentioned IC module will be explained in relation to the manufacturing method.

2 and 3 a to 3 d show the manufacturing process of a chip assembly to be attached to the multilayer wiring board 2. FIG. Here, the chip assembly refers to an IC chip 1 with flexible leads 5 attached thereto. First, as shown in FIG. 2, a film 9 made of polyimide resin with feed holes A formed therein is
After pasting the Cu foil with a heat-resistant adhesive, the Cu foil is processed by photoetching to form a flexible lead 5 having a dogleg-shaped bent portion.
Next, the polyimide film 9 is processed by photoetching to form a window B, which remains in the lead support portion 8. Thereafter, electroless Ni plating and electroless Au plating are sequentially applied to the flexible lead 5 in order to improve bondability.

On the other hand, IC chip 1 is manufactured by forming various circuit elements for LSI configuration on a Si wafer according to the usual method, and forming the required wiring between the circuit elements using metal such as Al. The wafer is obtained by subjecting the wafer to electrode formation processing for inner lead bonding, and then dividing the wafer into a plurality of pellets by dicing. Here, as the electrode formation process for inner lead bonding, SiO ₂ is deposited by sputtering on the entire surface of the Si wafer that has undergone the Al wiring process, and contact holes are formed in this SiO ₂ layer by photo-etching. After that, Cr--Cu--Au is deposited using a mask in this order, and then solder is deposited using a mask over the Cr--Cu--Au laminated electrode portion in a slightly larger area.
Next, Au is deposited on the backside of the wafer. Then, the solder electrode portion on the upper surface of the wafer is heated and melted to form a hemispherical shape. Thereafter, the IC chip 1 is completed through the usual steps of wafer inspection, dicing, and pellet sorting.

Inner lead bonding involves attaching an IC chip 1 that has undergone the electrode formation process described above to the inner end of a lead 5 supported by a tape 9 as shown in FIG.
This is the process of correspondingly bonding the solder electrodes. That is, the IC chip 1 is placed on the lead pattern with its upper surface facing down, and each solder electrode is arranged so as to be in contact with the inner tip of the corresponding lead 5. In this arrangement, after heating and melting the solder electrode with a heater chip,
Inner lead bonding is completed by solidifying. Thereafter, a normal electrical characteristic test is carried out by contacting the outer end of the lead 5 with a probe, and then the lead is cut to obtain a chip assembly as shown in FIG. 3a. In FIG. 3a, 8 is a lead support portion made of polyimide resin, and 10 is a solder electrode layer connecting the leads 5 and the chip 1. In FIG.

Next, as shown in Fig. 3b, the convex lower mold LD
Place the chip assembly of FIG. 3a on top of the
A flexible material SF such as rubber is layered on the IC chip 1 on the convex portion of the lower mold LD. Then, the upper mold UD ₁ presses the IC chip 1 through the soft material SF, and at the same time, the upper mold UD ₂ presses the outer ends of the leads 5 against the lower mold LD, thereby pressing the inner ends as shown in the figure. Right-angled bent portions opposite to each other are formed near the outer end and near the outer end. In this case, in order to achieve high-density mounting, the leads should be placed at an angle as close to a right angle as possible.
It is best to bend and shape. Such a molding process results in a chip assembly as shown in FIG. 3c.

After this, the lead support portion 8 made of polyimide resin is removed by appropriate chemical etching or the like.
A chip assembly as shown in FIG. 3d is obtained. Note that this removal process of the lead support portion 8 is preferably performed after outer lead bonding, which will be described later, so that bending of the lead 5 that may occur during handling can be minimized.

4a and 4b and FIG. 5 show the process of attaching the chip assembly configured as described above to the multilayer wiring board 2, and this attachment is accomplished by outer lead bonding. Ru. That is, the wiring layer 1 on the wiring board 2
Outer lead bonding is performed by overlapping the outer end of lead 5 on top of lead 1 through a brazing material such as solder, heating and melting the brazing material using a heater chip, and then solidifying it. , the attachment of the chip assembly to the wiring board 2 can be completed.

FIGS. 6-8 illustrate various shapes of flexible leads that can be used in the tip assembly described above, and which can be used in combination with the lead 5 described above to obtain the required springback pressure. It can be used as appropriate instead. The lead 5a in FIG. 6 has a width narrower at the dogleg-shaped bent portion than at other parts, and this allows the lead 5a to expand and contract more easily than the lead 5 described above. . Further, the lead 5b shown in FIG. 7 is also provided with notches P, Q, and R at the chip side root portion, central bent portion, and substrate side root portion, respectively, to facilitate expansion and contraction. Furthermore, the leads 5d shown in FIG. 8 have elasticity based on the fact that the aforementioned leads 5, 5a, and 5b are all bent in a plane substantially parallel to the end surface of the chip 1. On the other hand, the chip 1 is bent in a plane substantially perpendicular to the end face thereof to obtain elasticity. Although the lead 5c is bent in a step-like shape, it goes without saying that it can be modified as appropriate, such as in a protruding shape as shown by the broken line 5d.

Here, a specific example of the multilayer wiring board 2 will be explained.
As the material of the wiring board 2, for example, SiO ₂ glass, polyimide resin, fluororesin, alumina ceramics, etc. can be suitably employed, and as an example, a case where alumina ceramics is used will be described below. Alumina powder and auxiliary raw material powder are mixed with a binder to form a slurry, which is then cast into a sheet and dried to produce a processed base material (green sheet). Wiring layers such as power lines, ground lines, and signal lines are formed on this processed base material by a multiple printing method (thick film multilayer method) or a lamination method (thin film multilayer method), and through holes are also formed. Here, the metallization paste used is a heat-resistant metal such as a single layer of W or Mo, a layer of W and Mo laminated in this order, or a layer of Mo and Mn laminated in this order. Next, after finishing cutting the processed base material, it is fired and integrated, and then Ni plating is applied to the surface metallized layer.

Next, as shown in FIG. 9, the flange 4 and terminal pin 6 are attached by silver brazing or the like.
In FIG. 9, a metallized layer 11A on the back side of the wiring board 2 is formed by a brazing material layer 12 made of Ag-Cu eutectic silver solder.
and the flange 4. Next, electroless Ni plating and electroless Au plating are applied in this order to the entire exposed metal surface of the wiring board 2 to which the flange 4 and pin 6 are attached to ensure solderability.
After this, only flange 4 is energized to electrically Au.
Plating is applied to form an Au plating layer 14. This Au plating layer 14 is for obtaining good adhesion when sealing the flange 4 and the heat sink 3 together.

After that, solder is deposited with a mask on the bonding portion of the wiring layer 11 on the front side of the wiring board 2, and then the leads 5 are placed correspondingly thereon, and the aforementioned outer
Conduct lead bonding. Specifically, this is achieved by holding down the bonding portion with a heater chip and melting the solder on the substrate side, as in the case of inner lead bonding. In this case, the inner
It is necessary to take measures to prevent the solder in the lead bonding area from remelting, and one solution to this is to change the solder material used in the inner lead bonding area to the solder material used in the outer lead bonding area. The key is to select one with a lower melting point.

By the way, in FIG. 9, the heat sink 3 is
It is made of materials with good thermal conductivity such as Al, Cu, and Mo. For example, when it is made of Al, after Ni plating is applied to the entire surface, the surface other than the bonding surface with IC chip 1 is Heat dissipation fins 3A are formed by cutting. Then, this cutting process exposed the
The Al surface is anodized to provide corrosion resistance. After this, in order to relieve thermal stress and improve sealing performance,
A soft metal layer 15 is formed by In plating or the like. FIG. 10 shows an enlarged view of the state at this time, and in the same figure, 17 is below the soft metal layer 15.
The Ni plating layer and 20 indicate the Au vapor deposited layer on the back side of the IC chip 1, respectively. Note that instead of In plating, soft metal plating such as Sn, Pb, Bi, etc. can also be used. Further, the heat sink 3 is provided with a screw hole into which a bolt 7 is to be engaged later if necessary.

When fixing the heat sink 3 to the wiring board 2, the heat sink 3 is attached to the flange 4 using bolts 7. Here, flange 4 has a front diameter
A small hole of approximately 0.2 to 2 mm shall be provided.
As the bolt 7 is tightened, the IC chip 1
Move from the initial position indicated by the dotted chain line to the position indicated by the solid line in the direction indicated by the arrow. This is possible because the lead 5 is flexible or stretchable. Then, heating the whole module to about 160℃, In
The soft metal layer 15 and the Au plating layer 14 are melted together to form an In-Au joint 13,
This part is hermetically sealed. At the same time, the Au evaporated layer 20 on the back side of the chip also changes to the In layer 15 of the heat sink 3.
It melts together and forms a strong bond there. After this, the air in the space between the wiring board 2 and the heat sink 3 is replaced with dry air through the small hole previously provided in the flange 4, and then the small hole is closed by soldering or other methods. Seal and complete the IC module.
In addition, when repairing the IC module completed in this way, heat the entire unit to approximately 160°C and remove the bolts 7 to separate the heat sink 3 from the flange 4 at the joint 13, and also to separate the chip-heat sink between the chip and the heat sink. All you have to do is release the In-Au junction of the IC.
It is unlikely that the chip 1 or the leads 5 will be damaged. In particular, the leads 5 are bonded to the IC chip 1 or wiring board 2 using Pb-Sn solder that does not melt at temperatures around 160°C to prevent them from coming off or shifting due to heating during repairs. It is something that can be done.

FIG. 11 shows another example of a chip-heat sink bonding structure. In this structure, the IC chip 1 is large in size, and the IC chip is affected by thermal stress due to the difference in thermal expansion coefficient between the heat sink 3 and the IC chip 1. This is suitable for preventing cracks from entering the chip 1. In other words, there is a Si layer between the Al heat sink 3 and the IC chip 1.
A Mo plate 16 having a coefficient of thermal expansion similar to that of 1 is placed through a suitable soft metal layer 15 to relieve thermal stress, and the details of the joint are shown in Fig. 12. It's getting old. In FIG. 12, the same parts as in FIG.
Reference numeral 8b indicates an Au plating layer deposited on the Ni plating layers 17a and 17b, respectively, and 19a and 19b indicate soft metal plating layers such as In or the like deposited on the Au plating layers 18a and 18b, respectively. With such a configuration, in addition to obtaining the same effects as in the case of FIG. 10, insertion of the Mo plate 16 alleviates thermal stress and prevents the occurrence of cracks in the IC chip 1. It is something that provides action and effect.

Note that in the example of FIG. 11, the Mo board 16 is arranged separately for each IC chip 1;
This was done to minimize the entry of air bubbles into the joint between the aluminum heat sink 3 and the heat sink 3, and assuming that an appropriate degassing method is used, it is possible to It is also possible to place one Mo board over the entire surface.

In addition, in the above embodiment, the back surface of each IC chip 1 is bonded to the heat sink 3 via a brazing material to obtain a tight thermal bond, but the degree of thermal bonding may be sacrificed to some extent. If this is allowed, each
It is sufficient to simply bring the IC chips 1 into contact with each other under pressure, and in this case, the occurrence of chip cracks due to thermal stress can be almost eliminated.

Further, as the heat radiating body, various kinds of heat radiating bodies can be used in addition to the above-mentioned heat radiating body formed with heat radiating fins. For example, a radiator structure as shown in FIG. 13 is particularly suitable for a high-power IC module.
That is, the heat dissipating body 30 shown in FIG. 13 has a liquid refrigerant injected into a channel 31 in its main body from an inlet 32 and flowing therethrough, and flowing out from an outlet 33, and its cooling and heat dissipation effects are as described above. It is much larger than the heat sink 3.

[Brief explanation of the drawing]

FIG. 1 is a schematic sectional view of an IC module according to an embodiment of the present invention, and FIGS. 2 and 3 a to 3d are
It shows the manufacturing process of the chip assembly used in the above IC module, and Figure 2 is a top view;
3a to 3d are sectional views, FIGS. 4a and 4b, and 5 are sectional views, side views, and perspective views, respectively, showing the mounting structure of the chip assembly to the wiring board, and FIGS. 7 and 8 show various shapes of flexible leads that can be used in the above-mentioned chip assembly. FIGS. 6 and 7 are side views, FIG. 8 is a sectional view, and FIG. 9 is a side view. 10 is a cross-sectional view showing the mounting structure of the heat sink in the above IC module, and FIG. 10 is a chip in the structure shown in FIG. 9.
A cross-sectional view showing the details of the heat sink joint part, FIG.
A sectional view showing another example of the chip-radiator joint structure,
FIG. 12 is a sectional view showing details of the joining structure shown in FIG. 11, and FIG. 13 is a sectional view showing another example of the heat sink. 1... IC chip, 2... Wiring board, 3... Heat sink, 4... Fixing/sealing flange, 5... Flexible lead, 6... Terminal pin.

Claims (1)

[Scope of Claims] 1. A wiring board having a desired wiring layer formed on one main surface, and a heat dissipating device disposed opposite to the main surface of the wiring board and at a constant distance from the wiring board. an integrated circuit disposed between the wiring board and the heat radiator, the integrated circuit having one main surface facing the one main surface of the wiring board and the other main surface facing the heat radiator. The device electrically connects a plurality of electrodes on the one main surface of the integrated circuit device to the corresponding wiring layer of the wiring board, and the other main surface of the integrated circuit device An integrated circuit module comprising a plurality of leads that are elastically deformable so as to be pressed against the body. 2. The integrated circuit module according to claim 1, wherein the heat radiator is bonded to the other main surface of the integrated circuit device via a brazing material.