Abstract:
A monolithic microwave integrated circuit (MMIC) package comprises a MMIC die, a heat sink, an insulation substrate, and a sealing material. The MMIC die has an active region and a peripheral region. The heat sink is located in the active region. A plurality of bonding pads are located in the peripheral region. The insulation substrate has an opening and a plurality of transit ports. The opening is used to contain the heat sink and the transit ports are electrically connected to the bonding pads. The sealing material is filled between the insulation substrate and the MMIC die to cover the whole MMIC die so that the MMIC die is fixed to the insulation substrate and is protected.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the priority benefit of Taiwan application serial no. 90122432, filed Sep. 11, 2001. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a monolithic microwave integrated circuit (MMIC) package. More specifically, the present invention relates to a flip chip type MMIC package. 
     2. Description of the Related Art 
     Currently, the operational frequency of a common micro/millimeter wave integrated circuit is from about 3-30 GHz to 30-300 GHz. The functions and applications of the microwave/millimeter wave integrated circuit are limited to the package thereof. Therefore, to succeed in the MMIC market, a MMIC package having a high operational frequency, low parasitic capacitance and parasitic conductance, superior heat dissipation performance, compact body, low production cost, and an ability to mass production is required. 
     FIG. 1 is a schematic cross-sectional view of a conventional MMIC package. The package shown in FIG. 1 is a small outline integrated circuit (SOIC) package that is most widely used. The chip  104  is attached to a die region  106  of a leadframe  102  by surface mounting. A bonding wire  108  is used to electrically connect the chip  104  to the leadframe  102 . A sealing material  110  covers and fixes the wire  108 , the chip  104  and, a portion of the leadframe  106 . A package is formed after molding with a capsulatant  112 , which protects the electric properties from being deteriorated by moisture, dusts, or the like in the atmosphere. However, the leadframe may generate serious parasitic capacitance and parasitic conductance effects. 
     An approach to solve the above problem has been proposed. As shown in FIG. 2, a schematic cross-sectional view of another conventional MMIC package with an insulation substrate used as a carrier for a MMIC die  204  of a MMIC package  200 . The insulation substrate has an upper surface and a lower surface. The upper surface and the lower surface are provided with a plurality of contacts  202   a  and  202   b,  respectively. The contact  202   a  and the contact  202   b  are electrically connected through a via hole  202   c.  After the MMIC die  204  is attached to the insulation substrate  202 , a bonding wire  206  is used to electrically connect the contact  203  on the MMIC die  204  to the contact  202   a  on the insulation substrate. Finally, the sealing material  208  covers and fixes the MMIC die  204  and the bonding wire  206 . A package is formed after molding with a capsulatant  210 . 
     In the prior, the bonding wire may result in parasitic capacitance and parasitic conductance effects, which causes impedance and self-oscillation. 
     SUMMARY OF THE INVENTION 
     It is one object of the present invention to provide a MMIC package, which reduces the parasitic capacitance and the parasitic conductance. 
     It is another object of the present invention to provide a MMIC package, which has a heat sink bonded to an active region of the MMIC die to effectively dissipate heat. 
     It is still another object of the present invention to provide a MMIC package in which the electric connection between the chip and the insulation substrate is achieved by the flip chip technology instead of the wire bonding technology, resulting in a reduced package size. 
     It is still another object of the present invention to provide a MMIC package, which is applicable to the surface mount technology and is able to put into mass production. 
     In order to accomplish the above and other objects of the present invention, a monolithic microwave integrated circuit (MMIC) package comprising a MMIC die, a heat sink, an insulation substrate, and a sealing material is provided. The MMIC die has an active region and a peripheral region. The heat sink is located in the active region of the MMIC die. A plurality of bonding pads are located in the peripheral region. The insulation substrate has an opening and a plurality of transit ports. The opening is used to contain the heat sink, and the transit ports are electrically connected to the bonding pads. The sealing material is filled between the insulation substrate and the MMIC die to cover the whole MMIC die so that the MMIC die is fixed to the insulation substrate and is protected. 
     The transit ports of the insulation substrate are electrically connected to the bonding pads on the MMIC die by bumps. These bumps can be formed on the bonding pads of the MMIC die or on the transit port of the insulation substrate. 
     The heat sink that is used for the present invention is slightly smaller than the opening. 
     In one aspect of the present invention, the transit port of the insulation substrate further comprises a first contact, a second contact, and a via hole. The first contact is located on the upper surface of the insulation substrate. The second contact is located on he lower surface of the insulation substrate. The via hole is located in the insulation substrate and is used to electrically connect the first contact to the second contact. 
     In another aspect of the present invention, the transit port of the insulation substrate comprises a first contact and a second contact, which are not electrically connected to each other through a via hole. The first and second contacts disconnected to each other are used as dummy contacts. 
     The first contact on the upper surface of the insulation substrate is electrically connected to the bonding pad of the MMIC die. 
     The heat sink is bonded to the active region of the MMIC die by an adhesive layer. The adhesive layer can be made of a low dielectric material or a thermally conductive compound. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed. 
     The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principle of the invention. In the drawings, 
     FIG. 1 is a schematic cross-sectional view of a conventional MMIC package; 
     FIG. 2 is a schematic cross-sectional view of another conventional MMIC package; 
     FIG. 3 is a perspective view of an insulation substrate of a MMIC package to a preferred embodiment of the present invention; 
     FIG. 4 is a perspective view showing a MMIC bonded to a heat sink according to a preferred embodiment of the present invention; 
     FIG. 5 is a perspective view of a MMIC package according to a preferred embodiment of the present invention; 
     FIG. 6 is a schematic cross-sectional view of a MMIC package according to a preferred embodiment of the present invention; and 
     FIG. 7 is flow chart of producing a MMIC package according to a preferred embodiment of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Reference will now be made in detail to the present preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. Whenever possible, the same reference numbers are used in the drawings and the description to refer to the same or like parts. 
     A MMIC is mainly divided into a low power package with power lower than 1 mW and a high power package with power higher than 1 Mw. The high power MMIC package generates more heat than the low power package. The present invention is particularly suitable for the high power MMIC package. 
     FIG. 3 is a perspective view of an insulation substrate of a MMIC package according to a preferred embodiment of the present invention. The insulation substrate  300  is located in the central region and has an opening  302 . The opening  302  can be formed in ellipse, rectangle, circle or any suitable shape. The insulation substrate  300  has an upper surface  304  and a lower surface  306  opposite to the upper surface  304 . A plurality of first contacts  308  are provided on a peripheral region of the upper surface  304 . A plurality of second contacts  310  are provided on a peripheral region of the lower surface  306 . A plurality of via holes  312  are formed in the insulation substrate  300  to electrically connect the first contacts  308  and the second contacts  310 , respectively. The above first contact  308 , the second contact  310 , and the via hole  312  form a transit port  314 . 
     FIG. 4 is a perspective view of a MMIC package  400  after a MMIC die is bonded with a heat sink according to a preferred embodiment of the present invention. The MMIC die  401  has an active surface (not shown) on which a plurality of bonding pads  404  are provided in the peripheral region and a heat sink  408  is further provided in the central region. The heat sink  408  is bonded to the active surface by a non-conductive adhesive layer  406 . The heat sink  408  is formed of a thermally conductive compound such as BeO. The adhesive layer  406  has to be a low-dielectric-constant material that is also thermally conductive such as non-electrical-conductive epoxy. 
     With reference to FIGS. 3 and 4, the first contacts  308  on the insulation substrate  300  corresponds to the bonding pads  404  on the MMIC die  401  such that the bonding pads  404  on the MMIC die  401  are electrically connected to the first contacts  308  on the insulation substrate by means of metal bumps after chip flipping. Furthermore, the heat sink  408  bonded to the active region is slightly smaller than the opening in the insulation substrate. Therefore, the heat sink  408  bonded to the active region is located in the opening  302  in the insulation substrate  300  after chip flipping, thereby improving heat dissipation ability of the MMIC package. 
     FIG. 5 is a perspective view of a MMIC package according to a preferred embodiment of the present invention. The MMIC die  401  is subject to a flip chip process and put on the insulation substrate  300  to form a MMIC package  500 . The electric connection between the first contacts  308  of the insulation substrate  300  and the bonding pads  404  on the MMIC die  401  is achieved by bumps  502 , for example. After the first contacts  308  are electrically connected to the bonding pads  404 , a sealing material is poured into the gaps between the MMIC die  401  and the insulation substrate  300  to cover the whole MMIC die  401 . As a result, a package mold  504  is achieved. The package mold  504  serves to fix and protect the MMIC die  401 . 
     In this embodiment, the transit ports  314  on the insulation substrate  300  correspond to the bonding pads  404  on the MMIC die  401  so that the I/O signals of the MMIC die  401  are transmitted to the second contacts on the lower surface  306  of the insulation substrate  300  through the via hole  312 . Therefore, parasitic conductance effects caused by signal transmission in the insulation substrate  300  are avoided. 
     The insulation substrate  300  is exemplified for illustration of the present invention. However, the present invention is not limited to the above-specified example. The location and number of the transit ports  314  on the insulation substrate  300  may vary as desired. 
     Furthermore, the via holes  312  between the first contacts  308  on the upper surface  304  of the insulation substrate  300  and the second contacts  310  on the lower surface  306  can be optionally provided. More specifically, there is no via hole  312  between part of the first contacts  308  and part of the second contacts  310  for electric connection. The first contacts  308  and the second contacts  310  are not electrically connected to each other through any via hole that are used as dummy contacts. The dummy pads on the MMIC die  401  may help to distribute the stress due to chip flipping. 
     FIG. 6 is a cross-sectional view of a MMIC according to a preferred embodiment of the present invention. In the MMIC package  500 , the bonding pads  404  used for transmitting high frequency signals are connected to the transit ports  314  of the insulation substrate  300  by the bumps  502 . For example, the radio frequency signal is transmitted from ground-signal-ground (G-S-G) or signal-ground, (S-G) I/O ports on the MMIC die to the S-G-S or S-G I/O ports on the insulation substrate. The second contacts  310  exposed to the lower surface  306  of the insulation substrate  300  are used as I/O port of the MMIC package  500 . With such a structure, the electric properties of the MMIC package would not be deteriorated. Furthermore, the above package is applicable to the surface mount technology (SMT). 
     FIG. 6 shows a gap between the opening  302  and the heat sink  408  that can be filled with a sealing material in a subsequent molding process. The sealing material not only fixes the die to the insulation substrate, but also protects the package from external aggressions, especially moisture. 
     FIG. 7 is a flow chart of producing a MMIC package according to a preferred embodiment of present invention. First, a heat sink is bonded to an active region of the MMIC die (S 702 ) of a MMIC (S 700 ) having an active surface is provided. The heat sink effectively helps to dissipate the heat generated from the die. The I/O ports are formed on the insulation substrate (S 704 ). Then, an opening is formed in the insulation substrate ( 706 ). 
     Bumps are formed after the insulation substrate and the MMIC die have been prepared (S 708 ). The bumps can be formed on the bonding pads of the MMIC die or on the first contacts of the insulation substrate. In consideration of production cost and yield, the bumps are preferably formed on the first contacts to prevent damage of the MMIC die if the bumps fail. If the bumps on the insulation substrate fail, the deficient can be reworked. 
     After the bumps are formed, a flip chip process is carried out (S 710 ). The MMIC die is flipped and aligned with the insulation substrate in a desired manner. Then, a reflow process is performed (S 712 ) to complete the electric connection between the MMIC die and the transit ports of the insulation substrate. 
     Finally, a molding process is carried out (S 714 ). A sealing material is poured into the gaps between the MMIC chop and the insulation substrate to cover the whole MMIC die and then is cured to form a package mold  504 . The package mold  504  serves to fix and protect the MMIC die. During molding (S 714 ), the sealing material fills the bumps and the gap between the heat sink and the opening. After the molding process is completed, a cutting process is performed to accomplish a MMIC package (S 716 ). 
     In a light of foregoing, the MMIC package of the present invention has the following advantages over the prior art. The MMIC package obtained by the present invention using chip flipping has reduced parasitic capacitance and parasitic conductance. The heat sink bonded to the active region of the MMIC die effectively helps dissipate heat. Moreover, the electric connection between the die and the insulation substrate is achieved by the flip chip technology instead of the wire bonding technology, resulting in a reduced package size. Furthermore, the MMIC package obtained by the present invention is suitable for surface mount technology and is able to put into mass production. 
     It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the forgoing, it is intended that the present invention cover modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents.