Packaged semiconductor device having a shielding against electromagnetic interference and manufacturing process thereof

Abstract

A packaged device has a die of semiconductor material bonded to a support. An electromagnetic shielding structure surrounds the die and is formed by a grid structure of conductive material extending into the support and an electromagnetic shield, coupled together. A packaging mass embeds both the die and the electromagnetic shield. The electromagnetic shield is formed by a plurality of metal ribbon sections overlying the die and embedded in the packaging mass. Each metal ribbon section has a thickness-to-width ratio between approximately 1:2 and approximately 1:50.

Claims

1. A device comprising: a support that includes a recess delimited by a base portion and first and second sidewalls; an interference shield that includes: a conductive grid having a base in the base portion of the support, the base being exposed at a surface of the support, the conductive grid including a first vertical region in the first sidewall and a second vertical region in the second sidewall, the first and second vertical regions being coupled to the base; and a ribbon section coupled to the first vertical region at a first end and coupled to the second vertical region at a second end, the ribbon section having a curvature such that a length of the ribbon section is greater than a length of the surface of the conductive grid at the surface of the support, wherein the ribbon section and the conductive grid form an electromagnetic shield; and a semiconductor die located in the recess and enclosed by the interference shield, wherein the semiconductor die is between the base and the ribbon section, and wherein a portion of the semiconductor die is between the first vertical region and the second vertical region.

2. The device of claim 1 wherein the curvature of the ribbon section extends from the first end to the second end.

3. The device of claim 1 wherein the ribbon section includes a first portion including the first end, a second portion including the second end, and a third portion between the first portion and the second portion, the first and second portions having curvatures and the third portion being planar.

4. The device of claim 1 wherein the ribbon section has a concave side and a convex side, the concave side being closer to the semiconductor die than the convex side.

5. The device of claim 1 wherein the ribbon section includes a first shielding ribbon and a second shielding ribbon.

6. The device of claim 5 wherein the first and second shielding ribbons are spaced apart from and parallel to each other.

7. The device of claim 1 wherein the base is a copper mesh.

8. The device of claim 1, further comprising: a contact region in the base portion of the support, the semiconductor die electrically coupled to the contact region.

9. The device of claim 1 wherein the support is a printed-circuit board.

10. A method, comprising: forming a support that includes a recess and a conductive grid around the recess, a surface of the conductive grid being exposed at a surface of the support; positioning a first semiconductor die in the recess; and providing a shielding ribbon, wherein the shielding ribbon is coupled to the conductive grid, the shielding ribbon having a length this is greater than a length of the surface of the conductive grid at the surface of the support, the shielding ribbon and the conductive grid forming an electromagnetic shield.

11. The method of claim 10 wherein providing the shielding ribbon includes cutting a reel of ribbon to form ribbon sections and bonding the ribbon sections to the conductive grid.

12. The method of claim 11 wherein bonding the ribbon sections includes applying a bonding force to ends of the ribbon sections via a punch with ultrasound.

13. The method of claim 10, further comprising: electrically coupling the first semiconductor die to a contact region in the support, the contact region being electrically isolated from the shielding ribbon.

14. The method of claim 10, further comprising: positioning a second semiconductor die on the first semiconductor die, the second semiconductor die extending from the recess of the support.

15. A device, comprising: a support including a recess, a conductive grid in the support and around the recess, a surface of the conductive grid being exposed at a surface of the support; a semiconductor die in the recess and coupled to the support; and a shielding ribbon coupled to the surface of the conductive grid that is exposed at the surface of the support, the shielding ribbon having a length this is greater than a length of the surface of the conductive grid at the surface of the support, the shielding ribbon and the conductive grid forming an electromagnetic shield.

16. The device of claim 15 wherein the shielding ribbon includes a first shielding ribbon and a second shielding ribbon.

17. The device of claim 16 wherein the first and second shielding ribbons each are spaced apart from and parallel to each other, each shielding ribbon having a thickness-to-width ratio between approximately 1:2 and approximately 1:50.

18. The device of claim 15 wherein the conductive grid is a copper mesh and the support is a printed-circuit board.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

(1) For a better understanding of the present disclosure, preferred embodiments thereof are now described, purely by way of non-limiting example, with reference to the attached drawings, wherein:

(2) FIG. 1 is a perspective view of an embodiment of the present semiconductor device, prior to forming the packaging mass;

(3) FIG. 2 is a top plan view of the device of FIG. 1;

(4) FIG. 3 is a bottom view of the device of FIG. 1;

(5) FIG. 4 is a cross-section of the present finished device;

(6) FIG. 5 shows a ribbon reel that may be used for forming the device of FIG. 1;

(7) FIG. 6 shows the bonding operation;

(8) FIGS. 7 and 8 are cross-sections of different embodiments of the present device; and

(9) FIG. 9 shows a table of the width and thickness values of commercially available metal ribbons.

DETAILED DESCRIPTION

(10) FIGS. 1-3 show a semiconductor device 1 having a ribbon-type shielding structure, prior to forming the package.

(11) In detail, the device 1 comprises a support 2, for example a printed-circuit board PCB, having a first face (for example, a top face 2a) and a second face (for example a bottom face 2b). The support 2 has a reduced thickness in a central area for forming a cavity 3 facing the top face 2a (see also FIG. 4).

(12) A die 4 is fixed in the cavity 3 and accommodates an integrated electronic circuit or a micro-electro-mechanical device (not illustrated in detail). As may be seen in particular in the dashed line portion of FIG. 1 and in the cross-section of FIG. 4, the die 4 is connected to the outside via wired connections. Consequently, electrical connection wires 6 extend between a top surface 4a of the die 4 and the contact regions 8, facing the top surface 2a of the support 2, in a per se known manner.

(13) The contact regions 8 are arranged around the cavity 3 and are connected to conductive paths (not shown) provided on and/or within the support 2, as well as to through vias (not shown either) that connect the contact regions 8 to contact pads 9 on the bottom face 2b of the support 2. Alternatively, in a way not illustrated, the conductive paths may terminate at pads not shown on the top face 2a of the support 2 and/or wireless connection techniques of a known type, such as surface-mounting, may be used.

(14) A shielding structure or electromagnetic cage 10 surrounds the die 4. The shielding structure 10 comprises a grid 14 formed in the support 2 and a shield 15 overlying the support 2. The grid 14 and the shield 15 are electrically coupled together and grounded.

(15) The grid 14 comprises a peripheral strip 11, vertical regions 12 (FIG. 4) and a base portion 13, all of conductive material, for example metal, such as copper. For instance, if the support is a BGA/LGA (ball-grid array/land-grid array) substrate, the grid 14 may be typically a copper mesh formed on and through the substrate layers. Alternatively, the peripheral strip 11 and the base portion 13 may be formed over the faces 2a, 2b of the support 2.

(16) The peripheral strip 11 extends outward of the contact regions 8 (and thus outward of the die 4). In addition, the peripheral strip 11 faces the top face 2a of the support. In the example shown, in top plan view, the peripheral strip 11 has a quadrangular shape; in particular, it forms the sides of a square.

(17) The vertical regions 12 extend throughout the depth the support 2 between the top face 2a and the bottom face 2b of the substrate 2, and electrically connect the peripheral strip 11 to the base portion 13.

(18) The base portion 13 extends parallel to, and faces, the bottom face 2b of the substrate 2. The base portion 13 may be a continuous region, for example a plate, a non-continuous region with interruptions (as may be seen in the bottom view of FIG. 3), or a mesh.

(19) The conductive paths (not illustrated) that electrically connect the die 4 to the outside and extend between the contact regions 8 and the pads 9 may extend between pairs of vertical regions 12.

(20) The shield 15 is formed by a plurality of metal ribbon sections 16, which extend over the die 4, between opposite points of the peripheral strip 11. In the shown example, the ribbon sections 16 extend between two opposite sides of the quadrangle formed by the peripheral strip 11. The ribbon sections 16 are parallel to each other and spaced apart and are bonded at their ends 17 to the peripheral strip 11.

(21) As mentioned, the term ribbon sections 16 indicates sections of a continuous flat material, having a length greater than the width and a thickness much smaller than the other two dimensions, obtained by separation of a continuous reel of ribbon. In particular, each ribbon section 16 may have a width between one half and one tenth of the length, and a thickness of less than one half, for example one tenth or less of the width (for example, in commercially available ribbons, for widths that may be used for the present application, the width is between two and a half times and 40-50 times the nominal thickness of the ribbon).

(22) For instance, each ribbon section 16 may have a length L1 (see also FIG. 2) between 1 and 10 mm, a width L2 between 0.2 and 1 mm, and a thickness S (FIG. 4) between 80 and 100 m. Furthermore, the ribbon sections 16 may be set at a distance from each other between 0.1 and 0.5 mm.

(23) FIG. 9 shows, for example, a table that indicates values of width (on the abscissae) and of thickness (on the ordinates) of commercially available metal ribbons of the type that may be used with the present device. The internal hatched area represents the available values.

(24) With the dimensions indicated above, and on the hypothesis of having a die 4 with a height of 120 m and a cavity with a depth of 100 m, the ribbon sections 16 may have a maximum height H in the vertical direction (FIG. 4) between 0.1 and 1.5 mm as measured from the top face of the support 2.

(25) To reduce the overall vertical dimension of the ribbon sections 16, they may have a top central portion 16a that is flattened.

(26) A packaging mass 20 extends over the support 2, covering and embedding the die 4 and the shield 15, as well as the wires 6, filling the cavity 3, as may be seen in FIG. 4. The packaging mass 20, which forms a molded package, is a standard material for molded packages, typically plastic material, such as resin.

(27) Production of the device 1 is described hereinafter.

(28) Initially, the die 4 is manufactured according to usual semiconductor-machining techniques, cut and bonded to the support 2, which is also made in a per se known manner and accommodates the grid structure 14, the contact regions 8, and the contact pads 9. In general, in this step the support 2 is not yet singulated and is joined to other supports to form a supporting panel.

(29) For each die 4 the wired connections 6 are formed in a per se known manner, and the ribbon sections 16 are bonded to the peripheral strip 11. To this end, a reel 30 of metal ribbon is used, of the type illustrated in FIG. 5. The reel 30 may be of a type commonly available on the market, for example a reel of aluminum, gold or silver ribbon, or a reel of double-layered ribbon, such as aluminum and copper.

(30) One or more continuous ribbons 31 wound off one or more reels 30 are bonded to the respective support 2, individually or in parallel. In particular, for each continuous ribbon 31, after a first end has been bonded to a first side of the peripheral strip 11, the continuous ribbon 31 is passed over the die 4 and bonded on an opposite side of the peripheral strip 11. To this end, it is possible to use a bonding machine (or bonder) of the type used for forming power conductors in integrated devices, which are able to give a particular shape (or loop) on the ribbon section 16 (for example, to obtain the flattened portion 16a of FIG. 1). After bonding of the second end of the continuous ribbon 31, the latter is cut, thus separating the ribbon section 16 just bonded from the rest of the continuous ribbon 31. The process is then repeated for the subsequent dice 4. Bonding may be carried out using a punch, for example as the one designated by 35 in FIG. 6, applying pressure and ultrasound.

(31) For instance, for an aluminum wire having a width of 1 mm and a thickness of 0.1 mm, bonding may be carried out applying a pressure between 0.4 and 0.7 kg.sub.f, and for a time interval of 50-90 ms.

(32) In a per se known manner, the packaging mass 20 is molded on the entire panel of supports, and this is cut, to obtain a plurality of finished devices 1, as illustrated in FIG. 4.

(33) FIG. 7 shows a device 40 having a number of dice 4. In the example shown, two dice 4 (for example, a MEMS sensor and an ASIC integrating a logic for processing the data detected by the MEMS sensor) are arranged near each other, directly bonded to the support 2, within the cavity 3. Electrical connection wires 6 connect the dice 4 together and to the contact pads 8.

(34) Also here, the ribbon sections 16 extend between and are bonded to the peripheral strip 11 and form the shield 15. The packaging mass 20 encloses both of the dice 4, the connection wires 6, and the ribbon sections 16.

(35) FIG. 8 shows a device 50 wherein a number of dice 4 are arranged in a stacked configuration. In particular, a first die 4a is directly bonded to the support 2 and a second die 4b is arranged on top of, and bonded to, the first die 4a. Electrical connection wires 6 connect the dice 4a, 4b together and the first die 4a to the contact pads 8. For the rest, the device 50 of FIG. 8 is the same as the device 40 of FIG. 7.

(36) The device described herein has numerous advantages.

(37) In particular, it has a shielding structure built within the molded package 20 using standard processing steps in packaging of semiconductor devices.

(38) Additional parts to be produced and/or fixed after packaging are not utilized. Consequently, the shielding does not entail an increase in dimensions, in particular in the thickness, of the finished device.

(39) In particular, steps of plating or sputtering are not utilized to form external metal regions.

(40) Consequently, the costs of production are reduced and the solution may be applied to any type of substrate or lead frame with dedicated layout or design.

(41) Finally, it is clear that modifications and variations may be made to the device and to the manufacturing process described and illustrated herein, without thereby departing from the scope of the present disclosure.

(42) For instance, even though the shield 15 and the ribbon sections 16 have been represented completely embedded in the packaging mass 20, parts of them (for example, the higher central portions 16a) may surface and extend flush with the surface of the package.

(43) The die or dice 4 could be bonded to a flat support not provided with a cavity 3. In this case, the ribbon sections 16 would have a larger curvature.

(44) The peripheral strip 11 might not be continuous, but may be formed by a plurality of regions arranged peripherally; further, it could be formed on the bottom or on the side walls of the cavity 3.

(45) In the case of a multi-die package, the ribbon sections could be bonded also in intermediate areas, for example in areas arranged between the dice. In this case, instead of a single cavity 3, the support 2 could have a plurality of cavities or in any case raised portions that accommodate conductive regions belonging to the grid 14.

(46) Furthermore, intermediate bonding points could be provided also in the case of the single-die solution, and the intermediate bonding points could be obtained directly on the die. Intermediate bonding points could be provided also in the case of a number of dice arranged laterally to each other instead of or in addition to bonding points on raised portions of the support.

(47) The shield could be formed by two pluralities of ribbon sections arranged transverse, for example perpendicular, to each other, where the ribbon sections of one plurality extend over the ribbon sections of the other plurality.

(48) The base region 13 may not be facing the second face of the support 2; for example, it may be provided in a buried conductive layer that extends underneath the die 4.

(49) The various embodiments described above can be combined to provide further embodiments. These and other changes can be made to the embodiments in light of the above-detailed description. In general, in the following claims, the terms used should not be construed to limit the claims to the specific embodiments disclosed in the specification and the claims, but should be construed to include all possible embodiments along with the full scope of equivalents to which such claims are entitled. Accordingly, the claims are not limited by the disclosure.