WO2014110247A1

WO2014110247A1 - Integrated circuit module

Info

Publication number: WO2014110247A1
Application number: PCT/US2014/010860
Authority: WO
Inventors: Lee Han Meng@Eugene Lee; Anis Fauzi bin Abdyk AZIZ; Susan Goh Geok Ling; Ng Swee Tiang
Original assignee: Texas Instruments Japan Ltd; Texas Instruments Inc
Current assignee: Texas Instruments Japan Ltd; Texas Instruments Inc
Priority date: 2013-01-09
Filing date: 2014-01-09
Publication date: 2014-07-17
Anticipated expiration: 2015-07-09
Also published as: JP2016503240A; US8884414B2; US20140242755A1; US20140191381A1; CN104956782B; US9029194B2; JP6261055B2; CN104956782A

Abstract

An integrated circuit apparatus includes a generally flat die attachment pad (DAP) 130 positioned substantially in a first plane; and a generally flat lead bar 160 positioned substantially in a second plane above and parallel to the first plane and having at least one downwardly and outwardly extending lead bar lead 162 projecting therefrom and terminating substantially in the first plane; a top leadframe 12 having a plurality of generally flat contact pads 30 positioned substantially in a third plane above and parallel to the second plane and a plurality of leads 50 having proximal end portions 60 connected to the contact pads 30 and having downwardly and outwardly extending distal end portions 62 terminating substantially in the first plane; an IC die 72 connected to the top leadframe 12, and the DAP 130; and encapsulation material 200 encapsulating at least portions of the DAP 130, the lead bar 162, the top lead frame 12, and the IC die 72.

Description

INTEGRATED CIRCUIT MODULE

BACKGROUND

[0001 ] Integrated circuit (IC) packages typically include an IC die attached to a lead frame that enables contacts on the die to be attached to exterior circuits. The die and portions of the leadframe are often encapsulated in a covering of epoxy or other material that protects the die and leadframe. As IC dies have become smaller over time the number and density of contacts on the dies have increased. As a result, signal routing within the IC packages and heat dissipation from IC packages has become challenging. One recent development is the dual leadframe IC package in which more than one leadframe is provided in a single package to increase signal routing options. However, dual leadframe packages often pose added challenges of their own, such as a tendency of the two leadframes to make undesired electrical contact with each other. Such contact may result in a short circuit and package failure.

BRIEF DESCRIPTION OF THE DRAWINGS

[0002] Fig. 1 is a bottom perspective view of a top lead frame strip and flipchip dies.

[0003] Fig. 2 is a bottom perspective view of the lead frame strip of Fig. 1 with flipchips mounted on each lead frame.

[0004] Fig. 3 is a top perspective view of a top lead frame strip and bottom lead frame strip prior to attachment.

[0005] Fig. 4 is a top perspective view of attached top and bottom lead frame strips and flipchip dies attached therebetween and further showing the mounting of discrete circuit components on one top lead frame.

[0006] Fig. 5 is a top perspective view of attached top and bottom lead frame strips of Fig. 4 with discrete circuit components mounted on each top lead frame thereof. [0007] Fig. 6 is a top perspective view of three encapsulated dual lead frame assemblies such as shown in Fig. 5.

[0008] Fig. 7 is a cross-sectional side elevation view of an integrated circuit package singulated from a molded dual lead frame assembly such as shown in Fig. 6.

[0009] Fig. 8 is a bottom perspective view of the integrated circuit package shown in Fig. 7.

[0010] Fig. 9 is a top perspective view of the integrated circuit package shown in Figs. 7 and 8.

[001 1 ] Fig. 10 is a flow chart of one embodiment of a method of making integrated circuit modules.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

[0012] Fig. 1 illustrates a top lead frame strip 10 having integrally connected top lead frames 12, 14, 16, 18. The top lead frame strip 10 has a bottom surface 22 and a top surface 24, Fig. 3. Each top lead frame 12, 14, etc., has a plurality of generally coplanar contact pad portions 30 including individual contact pads 31 , 32, 33, 34, 36, 38, etc. Some of the contact pads, e.g., 31 , 33, etc., are mounted in a generally rectangular die mounting area 37 of each top lead frame, e.g., 12. Each lead frame also comprises a plurality of peripheral lead portions 50 which may comprise a plurality of relatively large lead portions 52, 54, 56, 58 and a plurality of relatively small lead portions 53, 55, 57, etc. One or more interior lead portions 59 may also be provided on each top leadframe 12, etc. Interior lead portion 59 may be attached to the die attachment pad (DAP) portion 130 of a bottom leadframe 1 10, described below. Each peripheral lead portion 50 has a proximal end 60 attached to at least one contact pad portion 30 and also comprises a downwardly and outwardly extending distal end 62. At least some of the peripheral lead portions 50 comprise connector extensions 64, 65, which may have a generally inverted U-shape or an inverted L-shape depending upon whether there is an adjacent connected leadframe. The connector extensions 64, 65 facilitate attachment of the top leadframe strips 10 to bottom leadframe strips 1 10, Fig. 3. The connector extensions 64, 65 may comprise other shapes adapted to facilitate connection between top and bottom leadframe strips 10, 1 10.

[0013] With reference to Figs. 1 and 2, a plurality of flipchips 72, 74, 76, 78 are mounted on the top lead frames 12, 14, 16, 18 respectively. Each flipchip has a first or active side 82 and a second or inactive side 84 as best seen in the cross-sectional view of Fig. 7. The active side 82 has a plurality of solder bumps 85, 87, 89, etc., formed thereon in a rectangular grid pattern. Each of the solder bumps is bonded to an associated contact pad portion, e.g., 31 , 33 in die mounting region 37 during reflow heating. The top lead frame strip 10 may be moved to a reflow oven (not shown) for soldering the flipchips 72, etc. to the top leadframes 12, etc., when in the configuration shown in Fig. 2, which is prior to attachment of the top lead frame strip 10 to a bottom lead frame strip.

[0014] Fig. 3 illustrates a bottom lead frame strip 1 10 having interconnected bottom lead frames 1 12, 1 14, 1 16, 1 18. The bottom lead frame strip 1 10 has a top surface 122 and a bottom surface 124. A die attachment pad (DAP) portion 130 is connected to a peripheral frame portion 132 which may be formed by a plurality of elongate frame members 134, 136, 138, 142. Each DAP portion 130 is circumscribed by an associated peripheral frame portion 132. The DAP portion 130 is connected to the surrounding peripheral frame portion 132 by a plurality of tie bars 152, 154, 156, 158. Each bottom lead frame 1 12, 1 14, etc., comprises an elongate lead bar 160 which is positioned in a plane parallel to and above a plane in which the DAP portion 130, peripheral frame portion 132 and tie bar portions 152, etc. are positioned. A first lead bar lead portion 162 and a second lead bar lead portion 164 are attached to opposite ends of the lead bar 160. Lead bar lead portions 162, 164 are integrally formed with and attached at distal ends thereof to an elongate side member 134 of the associated peripheral frame portion132. Thus, the distal end 168 at each lead bar lead portion 162, 164 is positioned substantially in the same plane as the DAP portion 130 and peripheral frame portion132. When the top and bottom leadframes, e.g., 16, 1 16, are connected as described below, the lead bar 160 is positioned substantially in the same plane as the top leadframe contact pad portions 30 and engages the bottom surface of at least one of the contact pad portions 30.

[0015] The top lead frame strip 10 after attachment of the flipchips 72, 74, 76, 78 thereto is attached, bottom surface 22 down, to the bottom lead frame strip 1 10 to form a dual leadframe strip 170. This is done, in one embodiment, by placing solder paste on the peripheral frame portions 132 and the lead bars 160 of the bottom lead frame strip 1 10 and then positioning the connector extensions 64, 65 of the top leadframe peripheral lead portions 50 in contact with the associated peripheral frame portions 132 and the bottom leadframe lead bars 160 into contact with the top leadframe contact pad portions 130. The top lead frame strip 10 "nests" on the bottom lead frame strip 1 10 through a positive and locating engagement of the lead portion connector extensions 64, 65 with the peripheral frame portions 132. The distal ends 62 of each of the top lead frame peripheral lead portions 50 and the lead bar lead portions 162, 164 act as vertical spacers in the dual lead frame strip assembly 170 shown in Fig. 4. The peripheral lead portions 50 of the top leadframes 10, 12, etc., also co-act with the peripheral frame portions 132 of the bottom leadframes 1 10, 1 12, etc. for proper lateral and angular positioning of the leadframes. The lead distal end portions 62 and the lead bar lead portions 162, 164 hold the top lead frame contact pad portions 30 at a predetermined height above the bottom lead frame DAP portions 130 and peripheral frame portions 132. The lead distal end portions 62 also hold the contact pad portions 30 in a generally laterally centered relationship with respect to the peripheral frame portions 132 of each bottom lead frame 1 12, 1 14, 1 16, 1 18.

[0016] Next, as further illustrated by Fig. 4, a plurality of discrete components which may be passive circuit components 182, 184, 186 may be mounted on the top surface of each top lead frame 12, 14, 16, 18. This may be accomplished by first applying solder paste to associated contact pad portions 30 of each top lead frame. The discrete circuit components 182, 184, 186 are then solder bonded to the associated top lead frames, e.g., 16, by placing the dual lead frame strip 170 in a reflow oven. In one method, the reflow heating of the solder paste beneath each discrete component 182, 184, 186 may take place at the same time as reflowing of the solder paste on the peripheral frame portions 132, etc. In another embodiment, the solder paste on the bottom lead frame is reflowed in a first operation before the discrete members 182, 184, 186 are placed on the associated top lead frames, e.g., 16. Fig. 5 illustrates the dual lead frame strip 170 after mounting of the discrete components 182, 184, 186 on each top lead frame 12, 14, 16,18.

[0017] Next, the dual lead frame assembly 170 of Fig. 5 is placed on a support frame 194, Fig. 6, and is moved to an encapsulation station such as a transfer mold station where mold compound is applied to the dual lead frame strip assembly 170 to provide an encapsulated dual lead frame strip 190. At least portions of the top and bottom lead frame strips 10, 1 10 and the flipchips 72, 74, etc. and the passive circuit components 182, 184, 186 are covered with encapsulating material 200 such as conventional mold compound which cures to provide a hard protective covering. The encapsulated dual lead frame strip 190 thus formed may be of various sizes and lengths depending upon the size and length of the top and bottom lead frames 10, 1 10 that were initially attached together. The encapsulated dual lead frame strip 190 illustrated in Fig. 6 has three, 2x2 dual lead frame assemblies 170 covered with encapsulating material 200. The encapsulated dual lead frame strip 190 has a generally flat top surface 192 and flat bottom (not shown) and side surfaces 195. The dashed lines shown at 196 represent the boundaries of three 4X4 encapsulated dual lead frame strips 190. Each 4X4 encapsulated leadframe assembly 190 is then singulated along the saw streets 100, 101 , 102, 103 (Figs. 1 -5) around each individual attached top and bottom leadframe assembly, e.g., 12,1 12.

[0018] As best shown in Figs. 7, 8 and 9, the singulation of an encapsulated dual lead frame strip 190 provides a plurality of individual integrated circuit (IC) packages 210, each having a flat top face 212, a flat bottom face 214 and a plurality of flat side faces 216. A bottom surface 131 of a DAP portion 130 is exposed at the bottom face 214 of each IC package. Also exposed on the bottom face 214 and side faces 216 are bottom surface portions 66 and terminal end surface portions 68 of the top lead frame lead portions 50 including smaller lead portions 53, 55, etc. as well as larger lead portions 52, 54, etc. Also, exposed are surface portions of bottom lead frame lead portions 162, 164. The exposed bottom surface 131 of the DAP portion 130 may be substantially flush with the bottom face 214 of the encapsulating layer 200. The exposed surfaces of the severed distal end portions 62 of the top leadframe peripheral leads 50 and of the severed distal end portion 168 of each lead bar lead portion 162, 164 may be substantially flush with the bottom face 214 and side faces 216 of the encapsulating layer 200.

[0019] As a result of the described method of attachment of each top leadframe, e.g., 12 to each bottom lead frame, e.g., 1 12, and the subsequent singulation and removal of outer ends of peripheral lead portions 50 and the attached peripheral frame portion 132, a significant gap 92, Fig. 7, is provided between the DAP portion 130 and the nearest outwardly extending peripheral lead portion 50. Thus, a common dual leadframe problem of top leadframes leads making undesired contact with and shorting out on the bottom lead frame is obviated. It will also be appreciated that by providing the described bottom leadframe lead bar configuration or similar structure that additional signal routing options are provided to the package designer. Although in the specifically described embodiments only one lead bar and two additional leads are provided it is to be understood that additional leads and thus additional signal routing options could be provided.

[0020] Fig. 10 illustrates a method of making integrated circuit packages. As shown in Fig. 10, the method includes, as shown at block 231 , providing a top

leadframe strip 10 comprising a plurality of integrally connected top leadframes 12, 14, etc. The method also includes, as shown at 232, mounting a plurality of flipchip dies 72, 74, etc., on the top leadframe strip 10 with solder bumps 85, 87, etc., of each flipchip die bonded to predetermined contact pad portions 30 on each of the top leadframes 12, 14, etc. The method further includes, as shown at 233, providing a bottom leadframe strip 1 10 comprising a plurality of integrally connected bottom leadframes 1 12, 1 14, etc., each having a central die attach pad (DAP) portion 130 and a peripheral frame portion 132. The method also includes, as shown at block 234, attaching the top leadframe strip 10 to the bottom leadframe strip 1 10 with a back face 84 of each flipchip die 72, etc., contacting the DAP portion 130 of each bottom leadframe 1 12, 1 14, etc., and with peripheral lead portions 50 of each top leadframe 12, 14, etc., attached to the peripheral frame portion 132 of each bottom leadframe 1 12, 1 14, etc.

[0021 ] Those skilled in the art to which the invention relates will appreciate that modifications may be made to the described embodiments, and also that many other embodiments are possible, within the scope of the claimed invention.

Claims

CLAIMS What is claimed is:

1 . An integrated circuit (IC) apparatus, comprising:

a generally flat die attachment pad (DAP) positioned substantially in a first plane; a generally flat lead bar positioned substantially in a second plane above and parallel to the first plane and having at least one downwardly and outwardly extending lead bar lead projecting therefrom and terminating substantially in the first plane;

a top leadframe comprising a plurality of generally flat contact pads positioned substantially in a third plane above and parallel to the second plane and a plurality of leads having proximal end portions connected to the pad portions and having

downwardly and outwardly extending distal end portions terminating substantially in the first plane;

an IC die comprising a plurality of electrical contacts connected to at least some of the plurality of contact pads of the top leadframe, and a surface attached to the DAP; and

encapsulation material encapsulating at least portions of the DAP, the lead bar, the top lead frame, and the IC die.

2. The apparatus of claim 1 , the IC die comprising a flipchip having a first side with a plurality of solder bumps thereon operably electrically connected to some of the plurality of contact pads of the top leadframe and having a second side opposite the first side comprising the surface connected to the DAP.

3. The apparatus of claim 1 , the top leadframe comprising at least one lead having a proximal end connected to at least one of the plurality of contact pads and a distal end connected to the DAP.

4. The apparatus of claim 1 , the generally flat lead bar being connected to the top leadframe.

5. The apparatus of claim 1 , at least one passive component electrically and physically connected to at least one of the contact pads on the top leadframe.

6. The apparatus of claim 1 , the encapsulation layer having a generally rectangular box shape with generally flat top, bottom and side faces, with a bottom surface of the DAP exposed at the bottom face and the distal end portions of the plurality of top leadframe leads and a distal end portion of the at least one downwardly and outwardly extending lead bar lead being exposed at the bottom face and the side faces of the encapsulating layer.

7. The apparatus of claim 6, the exposed bottom surface of the DAP being substantially flush with the bottom face of the encapsulating layer and the exposed surfaces of the distal end portions of the top leadframe leads and the distal end portion of the lead bar lead being substantially flush with the bottom face and the side faces of the encapsulating layer.

8. An integrated circuit (IC) apparatus, comprising:

a bottom leadframe comprising:

a generally flat peripheral frame portion positioned substantially in a first plane; a generally flat die attachment pad (DAP) portion circumscribed by the peripheral frame portion and positioned substantially in the first plane; and

at least one bottom leadframe lead portion having a first end connected to the peripheral frame portion and a second end positioned upwardly and inwardly from the peripheral frame portion;

a top leadframe comprising: a plurality of generally flat .contact pad portions positioned substantially in a second plane parallel to and above the first plane; and

a plurality of downwardly and outwardly extending top leadframe peripheral lead portions having proximal ends connected to the contact pads and distal ends connected to the bottom leadframe peripheral frame portion;

wherein the second end of the bottom leadframe lead portion is connected to the top leadframe.

9. The apparatus of claim 8, wherein the distal end portions of the outwardly extending top leadframe lead portions comprise integrally formed connector extensions, the peripheral frame portion nesting in the connector extensions of the lead portions at a predetermined distance from the contact pad portions.

10. A method of making integrated circuit (IC) apparatus, comprising:

providing a top leadframe strip comprising a plurality of integrally connected top leadframes;

mounting a plurality of flipchip dies on the top leadframe strip with solder bumps of each flipchip bonded to predetermined pad portions on each of the top leadframes; providing a bottom leadframe strip comprising a plurality of integrally connected bottom leadframes each having a central die attach pad (DAP) portion and a peripheral frame portion; and

attaching the top leadframe strip to the bottom leadframe strip with a back face of each flipchip die contacting the DAP portion of each bottom leadframe and with lead portions of each top leadframe attached to the peripheral frame portion of each bottom leadframe.

1 1 . The method of claim 10, further comprising encapsulating the flipchip dies and at least a portion of each top and bottom leadframe strip in mold compound.

12. The method of claim 1 1 , further comprising severing and removing the peripheral frame portion of each bottom leadframe and portions of the top leadframe lead portions that are attached thereto.

13. The method of claim 12, wherein the severing and removing comprises singulating the encapsulated flipchip dies and top and bottom leadframe strips into a plurality of IC packages that each have an exposed die pad surface and each have a plurality of exposed lead surfaces flush with a severed surface of a side face and the bottom face of the mold compound.

14. The method of claim 10, further comprising mounting at least one passive circuit component on each of the plurality of top leadframes.

15. The method of claim 10, wherein the attaching comprises solder bonding the top leadframe strip to the bottom leadframe strip including solder bonding a lead on each top leadframe to a DAP on each bottom leadframe.

16. The method of claim 15, further comprising singulating the top and bottom leadframe strips into a plurality of IC modules in a manner that exposes a cross- sectional portion of at least one lead that was integrally formed with the bottom leadframe and at least one lead that was integrally formed with the top leadframe.

17. The method of claim 10, wherein the providing a bottom leadframe strip comprises providing a plurality of integrally connected bottom leadframes each having a central die attach pad (DAP) and a peripheral frame assembly arranged in a generally rectangular configuration around and in substantially coplanar relationship with the DAP and with DAP tie members attaching the DAP to the peripheral frame.

18. The method of claim 17, wherein the providing a bottom leadframe strip comprises providing a plurality of integrally connected bottom leadframes each having a generally flat lead bar substantially located in a plane above the DAP and the peripheral frame and having at least one lead bar lead projecting therefrom and attached to the peripheral frame portion.

19. The method of claim 10, wherein the attaching the top leadframe strip to the bottom leadframe strip comprises nestingly and solderingly engaging the peripheral frame portion on each bottom leadframe of the bottom leadframe strip with end portions of leads on each top leadframe of the top leadframe strip.

20. The method of claim 19, further comprising singulating the attached top and bottom leadframe strips along saw streets positioned inwardly of the points of nesting and soldering engagement.