|Publication number||USRE37416 E1|
|Application number||US 08/558,979|
|Publication date||Oct 23, 2001|
|Filing date||Nov 13, 1995|
|Priority date||Mar 9, 1987|
|Also published as||DE3884019D1, DE3884019T2, EP0282124A2, EP0282124A3, EP0282124B1, US4926547, US5038198, USRE38037|
|Publication number||08558979, 558979, US RE37416 E1, US RE37416E1, US-E1-RE37416, USRE37416 E1, USRE37416E1|
|Inventors||Antonio P. Spatrisano, Luciano Gandolfi, Carlo Minotti, Natale Di Cristina|
|Original Assignee||Stmicroelectronics S.R.L.|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (19), Referenced by (2), Classifications (16)|
|External Links: USPTO, USPTO Assignment, Espacenet|
This is a continuation of application Ser. No. 08/152,253, filed on Nov. 12, 1993, now abandoned; which is a continuation of Ser. No. 07/864,492 filed on Apr. 7, 1992, now abandoned, which is a continuation of co-pending application Ser. No. 07/160,630 filed on 26 Feb. 1988 now abandoned.
The present invention relates to a method of manufacturing a modular semiconductor power device and to a device as obtained by such method.
In the manufacture of modular semiconductor power devices, as in the manufacture of numerous other components, an important target is to produce extremely reliable products using sample simple and inexpensive procedures.
The known semiconductor power devices involve complex and costly procedures, both from the point of view of the individual components necessary for constructing them and from the standpoint of their assembly and reciprocal insulation.
Some of these known devices are described in U.S. Pat. No. 4,518,982. This patent gives a detailed description of a modular power device whose manufacturing process consists of soldering one or more semiconductor chips onto a flat portion of a first electrode (which also serves as a heat sink), soldering other electrodes (possibly containing other chips) onto the flat portion by means of a dielectric adhesive material, electrically connecting the various chips and electrodes, encapsulating the device in resin, and electrically insulating the heat dissipating surface by means of a further layer of insulating material.
The object of this invention is to provide a particularly reliable modular power device obtained by means of an extremely simple and not very expensive assembly procedure, according to a highly flexible manufacturing method and with components which, although extremely limited in number, can be used to create various circuit arrangements and layouts, always using the same tools and always maintainins maintaining an identical external geometrical configuration of the devices obtained.
According to a particular feature of the manufacturing method, the reciprocal insulated insulation of the electrodes and their encapsulation are carried out in a single step. The manufacturing method according to the invention for making a modular semiconductor power device comprising one or more semiconductor chips, a metal plate for dissipating heat generated by the Joule effect, a plurality of electrodes constituting the signal and power terminals of the device, and a resin encapsulation, comprises soldering the chip or chips onto one or more plates of electrically conductive material;
positioning the plate or plates on a plane substantially parallel to the aforesaid heat dissipating plate and close to the latter;
blanking, from a single sheet of conductive material, a one-piece frame designed to constitute the power and signal terminals, the blanking enabling temporary connections to be kept between the portions of the terminal conductors designed to remain outside of the resin encapsulation;
soldering the inner ends of the terminals to points arranged for the connection to the aforesaid chips;
encapsulating with insulting insulating resin all the active parts of the device, leaving uncovered the outer surface of the plate and the portions of the terminals involved with the aforesaid temporary connections; and
shearing the temporary connections.
Each sheet can be made of copper and that the latter, before the chips are soldered onto it, can be placed in a plate consisting of three layers soldered directly onto each other, in which the first layer is made up of the sheet and copper strips insulated from the sheet itself. The intermediate layer consists of an alumina plate and the third layer consists of a sheet of copper substantially equal in size or slightly smaller than the intermediate layer. The aforesaid points of connection are situated on the aforesaid sheets and strips, the soldering of the inner ends of the terminals to the aforesaid points is preceded by the soldering of wires connecting the chips to the aforesaid strips.
The sheet can be soldered onto the internal surface of the plate and the connections between chips and strips can be made by means of ultrasound soldering of aluminum wires.
The aforesaid points of connection with the chips can be located on the aforesaid sheets and on wettable metal coatings on the surface of the chips.
After blanking of the one-piece frame and before the aforesaid soldering of the inner ends of the terminals to the points of connection, the inner ends of the terminals can be bent in a direction perpendicular to the plane of the frame.
After the encapsulation and the shearing of the temporary connections of the one-piece frame, the terminals designed to perform the function of signal terminals can be bent in a direction perpendicular to the base plate, while the terminals designed to perform the function of power terminals can be bent over the capsule in a direction parallel to the base plate itself.
The features of the invention will be more clearly evident from the following description and the accompanying drawing in which:
FIG. 1 is an exploded view of the base plate and the substrates supporting the chips: ;
FIGS. 2a and 2 b, respectively, are a side view and a cross-sectional view of the base plate of FIG. 1;
FIGS. 3a, 3 b and 3 c, respectively, are bottom, top and cross-sectional views of a substrate of FIG. 1;
FIG. 4 is a view of the base plate of FIG. 1 after the substrates and the chips have been joined to it, and after the electrical connections between chips and metal coating of the substrates have been made;
FIG. 5 is a perspective view of the one-piece frame for obtaining the external terminals and their connections with the metal-coating of the substrates;
FIG. 6 is a plan view of the flattened frame from which the frame of FIG. 5 was obtained;
FIG. 7 is a perspective view of the modular device after the resin encapsulation has been carried out by molding; and
FIGS. 8a, 8 b and 8 c are respective perspective top and bottom views and a plan view of the finished device.
In FIG. 1 the base plate 11 of the device acts as a heat sink as well as a support and fastener for the device itself. It is made of heat-conductive metal with high mechanical strength. The holes A in it serve to secure it, by means of screws, onto the external heat spreader, while the grooves V serve to absorb any possible deformation of the base plate due to the high tightening torque, thereby preventing them from being transmitted to the central portion of the plate.
The S-shaped recesses M, on the sides (see the side and cross-sectional views of the plate shown in FIGS. 2a and 2 b) serve to ensure a better adhesion of the subsequently applied resin encapsulation, as is explained more clearly further on with reference to FIG. 8b.
FIG. 1 also shows the components 12 and 13, which are two chip-supporting substrates, which are soldered onto the base plate 11 by means of the layers of solder 14.
As illustrated in FIGS. 3a, 3 b and 3 c (bottom, top and cross-sectional views of a substrate) each substrate is composed of a quadrangular-shaped thin medial layer 31 of alumina (less than 1 mm thick), with thin copper plates soldered directly onto its two lateral faces. More precisely, soldered onto the face destined to lie facing the upper face of the base plate 11 is a single copper plate 32, which is also quadrangular in shape but with slightly smaller dimensions than those of the layer of alumina, while the other face is provided with a rectangular plate 33, for supporting the chips and for the connections with an external electrode, and, on either side of said plate 33, narrower plates (lateral strips) 34, 35 and 36 designed both for soldering the conductor for connection with the chips, and for soldering other external electrodes.
FIG. 4 shows the device 41 as it appears after the two substrate substrates have been soldered onto the base plate, the chips have been soldered onto the larger upper copper plates b and f, and the electrical connections have been carried out between the chips and the lateral strips a, c, d, e, g, and h. The latter connections are obtained by ultrasonic soldering with aluminum wire.
FIG. 5 shows a copper frame 51 designed to constitute the external terminals and the connections of the latter with the lateral strips and the plates f and b of FIG. 4. The frame of FIG. 5 is obtained by blanking from a copper sheet and by subsequently bending the terminal portions downwards, said terminal portions being subsequently soldered onto the lateral strips and the plates f and b.
FIG. 6 shows a plan view of the frame of FIG. 5, as it appears after being blanked from the copper sheet and before the bending of the terminal portions, which are indicated respectively by h, g, e, d, c, a, f, and b. After being bent downwards, the terminal portions are then soldered respectively onto the strips h, g, e, d, c, and a, and onto the plates f and b of 41. After the frame 51 has been soldered onto the device 41, the device is encapsulated by means of a molding process with insulting insulating resin (e.g. thermosetting epoxy resin), preferably of the low-stress type.
After the moldings phase, the device has the appearance shown in FIG. 7. At this point, in order to complete complete the device, it is necessary to shear the external temporary connections between the terminals, corresponding to the portions 61 illustrated in dotted cross-hatched lines in FIG. 6, and then bend the signal terminals upwards to a vertical position, and the power terminals inwards.
The finished device takes on the appearance of FIG. 8a (top perspective view) and of FIG. 8b (bottom perspective view), in which 81, 82, 83 and 84 indicate the signal terminals and 85, 86 and 87 indicate the power terminals.
As shown in FIG. 8b, the resin encapsulation ends, from below, are flush with the lower surface of the base plate 11, which can consequently be secured in direct contact with the supporting metal structure on which it is designed to be placed, thereby ensuring efficient dissipation of the heat. The same figure clearly shows the function of the S-shaped recesses M on the base plate (see FIGS. 1 and 2b). In fact, on completion of the device, they are completely embedded in the resin body, so as to constitute two areas for anchoring and ensuring an efficient grip of the resin.
As shown in FIG. 8c (plan view of the device), after the bending, the terminal holes of the three power terminals 85, 86 and 87 come to rest exactly above the three hexagonal nuts embedded in the resin, so as to enable the electrical connection with the external connecting rods.
The foregoing description gives a clear idea both of the versatility of the method of the invention and of the simplicity of the assembling procedure. In fact, it is clear that:
with the substrates of FIG. 1 and FIG. 3, it is possible to use chips of different number and sizes, to achieve different connections of the chips with the lateral strips, and to obtain soldered strips with different geometrical layouts;
the one-piece of FIG. 5 and FIG. 6 can also be made with different geometrical layouts, to enable it to adapt to the different geometrical layouts of the aforesaid soldered strips, and to the different electrical functions of the device;
the procedures for soldering the conductors connecting the chips to the metal strips and the external electrodes to the metal chip-supporting strips or plates are simplified due to the flat disposition of the soldering points and to the fact that the inner ends of the electrodes are soldered when they are still firmly secured to each other by the aforesaid temporary connections; and
due to the fact that the chips are soldered onto coplanar plates and to the presence of the temporary connections between the electrodes it is also possible to carry out the encapsulation and reciprocal insulation of the electrodes in a single step. A further advantage, in addition to those mentioned previously, is related to the particular structure of the substrate chosen for soldering the chips as well as that related to the type of resin used for the encapsulation. In fact, these substrates, which consist of a layer of alumina with copper plates soldered directly onto both faces, are characterized by thermal expansion coefficients very similar to those of silicon. This reduces to a minumum the thermomechanical stress which would otherwise be transmitted to the chips due to the differential expansion of silicon and copper (other embodiments envisage the insertion, between the chips and the supporting copper plates, of layers of material, such as for example, molybdenum, having an expansion coefficient lying half way between those of silicon and copper, which however complicate the assembling and lower the thermal performance).
The use of a low-stress type of resin helps to limit the stress transmitted to the chips even in the case of chips of very large dimensions.
It is also clear that numerous modifications, adjustments, variations and substitutions may be made to the embodiments previously described by way of example, always remaining within the spirit of this invention and its scope. For example, the wires connecting the chips to the metal strips of the substrates can be by direct soldering between the inner terminal portions of the one-piece frame and the chips, whenever the latter have wettable metal coatings. These internal portions can then be soldered to points (P) of connection with the chips situated on the aforesaid plates 33 and strips 34, 35, 36 (as in the case illustrated in FIGS. 4 and 5), or situated on the same plates and on wettable metal coatings on the surface of the chips.
Likewise, the chip-supporting substrates could have a different structure from that previously described and the insulation between the chips and the dissipator could be achieved by means of a layer of the encapsulating resin itself—which in this case should be of high thermal conductivity—instead of by a layer of alumina.
|Cited Patent||Filing date||Publication date||Applicant||Title|
|US4026008 *||May 19, 1975||May 31, 1977||Signetics Corporation||Semiconductor lead structure and assembly and method for fabricating same|
|US4102039 *||Feb 14, 1977||Jul 25, 1978||Motorola, Inc.||Method of packaging electronic components|
|US4106052||Sep 1, 1977||Aug 8, 1978||Semikron Gesellschaft Fur Gleichrichterbau Und Elektronik M.B.H.||Semiconductor rectifier unit having a base plate with means for maintaining insulating wafers in a desired position|
|US4396936||Dec 29, 1980||Aug 2, 1983||Honeywell Information Systems, Inc.||Integrated circuit chip package with improved cooling means|
|US4518982 *||Sep 20, 1983||May 21, 1985||Motorola, Inc.||High current package with multi-level leads|
|US4530152 *||Apr 1, 1983||Jul 23, 1985||Compagnie Industrielle Des Telecommunications Cit-Alcatel||Method for encapsulating semiconductor components using temporary substrates|
|US4558510 *||Mar 23, 1984||Dec 17, 1985||Tokyo Shibaura Denki Kabushiki Kaisha||Method of producing a semiconductor device|
|US4615031||Jul 15, 1983||Sep 30, 1986||International Standard Electric Corporation||Injection laser packages|
|US4635356 *||Aug 15, 1985||Jan 13, 1987||Kabushiki Kaisha Toshiba||Method of manufacturing a circuit module|
|US4675989 *||Apr 7, 1986||Jun 30, 1987||Amp Incorporated||Method of making an electrical circuit package|
|US4722060 *||Mar 22, 1984||Jan 26, 1988||Thomson Components-Mostek Corporation||Integrated-circuit leadframe adapted for a simultaneous bonding operation|
|US4783428 *||Nov 23, 1987||Nov 8, 1988||Motorola Inc.||Method of producing a thermogenetic semiconductor device|
|US4807018 *||Oct 26, 1987||Feb 21, 1989||Sgs Microelettronica S.P.A.||Method and package for dissipating heat generated by an integrated circuit chip|
|DE3336979A1 *||Oct 11, 1983||Apr 26, 1984||Mitsubishi Electric Corp||Turn-off thyristor module|
|DE3516995A1 *||May 10, 1985||Nov 14, 1985||Mitsubishi Electric Corp||Semiconductor device|
|EP0282124A2 *||Feb 29, 1988||Sep 14, 1988||SGS-THOMSON MICROELECTRONICS s.r.l.||Method for manufacturing a modular semiconductor power device and device obtained thereby|
|FR2495376A1 *||Title not available|
|GB1255073A *||Title not available|
|GB2099742A *||Title not available|
|Citing Patent||Filing date||Publication date||Applicant||Title|
|US8422243 *||Dec 13, 2006||Apr 16, 2013||Stats Chippac Ltd.||Integrated circuit package system employing a support structure with a recess|
|US20080142938 *||Dec 13, 2006||Jun 19, 2008||Stats Chippac Ltd.||Integrated circuit package system employing a support structure with a recess|
|U.S. Classification||29/841, 29/832|
|International Classification||A61K39/175, C12N7/06, H01L23/495, H01L25/065, H01L21/50|
|Cooperative Classification||Y10T29/49146, Y10T29/4913, H01L2924/0002, H01L21/50, H01L23/49575, H01L25/0655|
|European Classification||H01L23/495L, H01L21/50, H01L25/065N|