PACKAGED SEMICONDUCTOR DEVICE HAVING ATTACHED CHIPS OVERHANGING THE ASSEMBLY PAD
A semiconductor device (200) comprising a semiconductor chip (201) has an electrically active side (201a) and an opposite electrically inactive side (201b); the active side bordered by an edge having a first length (202a), and the inactive side bordered by a parallel edge having a second length (202b) smaller than the first length; a substrate has an assembly pad (210) bordered by a linear edge having a third length (210a) equal to or smaller than the first length; the inactive chip side attached to the pad so that the edge of the first length is parallel to the edge of the third length; the active side of the attached chip forms an overhang over the pad, when the third length is smaller than the first length.
Embodiments of the invention are related in general to the field of semiconductor devices and processes, and more specifically to the structure and fabrication method of packaged semiconductor devices with single or stacked chips overhanging the assembly pad.
DESCRIPTION OF RELATED ARTIt is common practice in fabricating semiconductor devices that semiconductor chips are attached to substrate pads with an adhesive material such as a solder or a polymeric compound. In this attachment process, first a controlled amount of adhesive material is deposited on the pad, and then the chip is placed on top of the material while enough pressure is applied to distribute the material uniformly and allow a small amount of material to bulge from the chip edges. For the visual process quality control by inspectors, this bulge is indispensable as a signal of defect-free assembly.
As a consequence of this generally accepted quality control practice, chip areas have to be at least slightly smaller than assembly pad areas to allow enough space for the bulges of adhesive material. Whenever a new product requires a larger chip area than the preceding product, a new generation of assembly pads has to be provided with a pad area larger than the one required before. In order to satisfy this need, time and money have to be expended.
SUMMARYApplicants realized that the ongoing market pressures for greater flexibility in satisfying customer needs and for faster product turn-around time need a quantum jump in assembling semiconductor chips on substrate pads. Applicant saw that until now a semiconductor chip has been considered an inseparable unit, wherein the active side and the passive side (which is to be attached) form an immutable hexahedron with straight sidewalls.
By considering the passive chip side independent from the active side, applicants solved the problem of requiring an enlarged assembly pad every time the chip size is increased, when they discovered a methodology of diminishing the area of the passive side for the attachment process while retaining the area of the active side for the circuitry.
In the methodology, the singulation of chips from a semiconductor wafer is performed in two steps. The inactive side of the wafer receives a grid of linear grooves of a first width and a depth smaller than the wafer thickness. Then, the active side of the wafer receives a matching grid of linear slits of a second width smaller than the first width and a depth merging the slits with the respective grooves, thereby singulating chips from the wafer.
As a result of the two-step singulation process, each chip has a large-area active side while exhibiting an overhang over the smaller-area passive side. As a hexahedron with concave curved sidewalls, the chip maintains the active side required by the circuitry while obtaining a passive area acceptable to the available assembly pad.
In some devices, the inactive or un-patterned side may be smaller than the active or patterned side not along all four edges, but only along one, two, or three edges. In still other devices, the shorter lengths may not be parallel to the greater lengths, but form an angle relative to the greater lengths.
In other embodiments, the semiconductor chip may have triangular sides or any other geometric configuration. In all cases, though, the electrically active side has a larger area than the electrically inactive or passive area, and the analogous side edges are greater for the active side than for the inactive side.
As
In the device example of
In contrast,
Similar to exemplary device 100,
As
Another embodiment of the invention, generally designated 300, is illustrated in
Device 300 further has a second semiconductor chip 305 with an electrically active side 305a and an opposite electrically inactive side 305b. The active side is bordered by an edge having a third length 306a, which may be equal to, smaller than, or greater than the first length 302a; in the example of
As
The second chip 305 is attached to suitable site of a substrate. The substrate may be the chip pad 310 of a metal leadframe, as shown for the exemplary device 300. Alternatively, the site may be an attachment pad of a laminated substrate, or it may be the metallized pad of a board. In these and other examples, the substrate provides an assembly pad bordered by a linear edge having a fifth length. In
Embodiments include devices wherein the third length is equal to or smaller than the first length and the active side of the attached first chip forms an overhang over the active side of the second chip. Further, embodiments include devices wherein the fifth length is smaller than the third length and the active side of the attached second chip forms an overhang over the top pad side.
As
In the device example of
Another embodiment of the invention is a method for fabricating a semiconductor chip with an overhang of the chip side containing the active elements over the opposite side free of active elements. The method starts by providing a semiconductor wafer of a first thickness, which has an electrically active side and an opposite electrically inactive side. The active side includes a plurality of sites, which will become chips, containing elements such as transistors, diodes, and integrated circuitry; the fabrication of the active elements is completed. The sites have linear borders between adjacent chips. As an example, the sites may have rectangular configuration with linear borders between the each adjacent site.
In the next process, the inactive wafer side is subjected to a backgrinding technique in order to reduce the first thickness of the wafer to a second thickness smaller than the first thickness.
Next, a grid of linear grooves is formed in the semiconductor material of the inactive wafer side. The grooves are arrayed in parallel rows intersecting with parallel columns so that the rows and columns are at right angles to each other. The technique to form the grooves is selected from a group including laser sawing, mechanical sawing with a relatively wide blade, chemical etching, and hitting with liquid jets. The grooves such generated have edges spaced by a first width and a depth smaller than the second thickness. Dependent on device type, first width may be between 0.2 mm and 1.0 mm or more. Preferably, the grooves have a rounded bottom; alternatively, the bottom may be more triangular or cornered.
In the next process, a matching grid of linear slits is formed on the active wafer side. The slits are arrayed in parallel rows intersecting with parallel columns. The preferred technique to form the slits is a mechanical saw with thin blade. The slits have edges spaced by a second width smaller than the first width and a depth deep enough so that the slits can merge with the respective grooves. Preferably, each slit is administered about in the middle of the respective groove penetrating the wafer from the opposite side. After the merger of slit and grooves, the merged slits and grooves represent effective cuts for singulating discrete rectangular chips from the wafer.
The resulting chips have overhangs of the active side over the inactive side. Each singulated chip has an electrically active side bordered by an edge having a first length, and an opposite electrically inactive side bordered by a parallel edge having a second length smaller than the first length.
Another embodiment of the invention is a method for fabricating a semiconductor device with a single chip with an overhang attached to a substrate. The method starts by providing a semiconductor chip with an electrically active side and an opposite electrically inactive side. The active side is bordered by an edge having a first length, the opposite inactive side is bordered by a parallel edge having a second length smaller than the first length. Consequently, the active side forms an overhang over the inactive side. For some exemplary chips, the second length may be 2.25 mm and the first length 3.55 mm, creating a relatively long overhang of 0.65 mm on each chip end.
Next, a substrate is provided, which has an assembly pad bordered by a linear edge having a third length equal to or smaller than the first length. A preferred substrate is a metal leadframe. Alternatively, the substrate may made by laminating metal and insulating layers into a multilayer composite. In addition to the assembly pad, the substrate has a plurality of leads, which serve a terminals of the completed device; the leads are in the proximity of the pad and may surround the pad.
In the next process, the inactive chip side is attached to the pad so that the edge of the first length is parallel to the edge of the third length. Thereafter, the chip is connected to respective substrate terminals by bonding wires. Then, the chip and the bonding wires are encapsulated in a packaging compound, for instance in an epoxy-based molding compound.
Another embodiment of the invention is a method for fabricating a semiconductor device having a set of vertically stacked chips with overhangs attached to a substrate. The method starts by providing a first semiconductor chip with an electrically active side and an opposite electrically inactive side. The active side is bordered by an edge with a first length, the inactive side is bordered by a parallel edge having a second length smaller than the first length. As a consequence, the active side forms an overhang over the inactive side. For some exemplary chips, the second length may be 2.25 mm and the first length 3.55 mm, creating a relatively long overhang of 0.65 mm on each chip end.
Next, a second semiconductor chip is provided, which has an electrically active side and an opposite electrically inactive side, the active side bordered by an edge having a third length equal to, smaller, or greater than the first length, the inactive side bordered by a parallel edge having a fourth length smaller than the third length.
In the next process, the inactive chip side of the first chip is attached to the active side of the second chip so that the edge of the first length is parallel to the edge of the third length. Consequently, the first chip is vertically stacked on the second chip, forming a vertical chip set. For devices wherein the third length is equal to or smaller than the first length, the active side of the attached first chip forms an overhang over the active side of the second chip. After the stack set has been assembled, there has to be enough space between the overhang of the first chip and the active side of the second chip to span bonding wires from the second chip to substrate leads without contact between the wires and the underside surface of the overhang.
Next, a substrate is provided, which has an assembly pad bordered by a linear edge with a fifth length equal to or smaller than the third length. The substrate may be a metal leadframe or a laminated board. The substrate includes a plurality of leads or terminals in the proximity of the assembly pad. The inactive chip side of the second chip is attached to the pad so that the edge of the third length is parallel to the edge of the fifth length. For devices wherein the fifth length is smaller than the third length, the active side of the attached second chip forms an overhang over the pad. As mentioned, the adhesive layer is preferably formed by a conductive polymer, but may also be formed by solder; in both cases, the preferred thickness of the adhesive layer is about 0.025 mm.
In the next process, the first chip and the second chip are connected to respective substrate terminals by bonding wires. Thereafter, the chips and the bonding wires are encapsulated in a packaging compound, preferably by an epoxy-based molding compound.
While this invention has been described in reference to illustrative embodiments, this description is not intended to be construed in a limiting sense. Various modifications and combinations of the illustrative embodiments, as well as other embodiments of the invention, will be apparent to persons skilled in the art upon reference to the description. As an example, the invention applies to products using any type of semiconductor chip, discrete or integrated circuit, and the material of the semiconductor chip may comprise silicon, silicon germanium, gallium arsenide, or any other semiconductor or compound material used in integrated circuit manufacturing.
For products with more than one chip, the invention applies to two, three or more chips. The invention applies to products with chips of equal thickness and to products, wherein the chips have different thicknesses. The invention applies to products with chips of equal overhangs, and to products, wherein the chips have different overhangs.
As another example, the invention applies to any semiconductor device family which uses QFN/SON leadframes, or a leadframe with pins. The invention further applies to any amount of overhang over to the attachment pads/
It is therefore intended that the appended claims encompass any such modifications or embodiment.
Claims
1. A semiconductor device comprising:
- a semiconductor chip having an electrically active side and an opposite electrically inactive side, the active side bordered by an edge having a first length, the inactive side bordered by a parallel edge having a second length smaller than the first length;
- a substrate having an assembly pad bordered by a linear edge having a third length smaller than the first length; and
- the electrically inactive side attached to the pad, wherein the electrically active side of the attached chip forms an overhang over pad.
2. (canceled)
3. The device of claim 1 wherein the overhang is along one edge of the attached chip.
4. The device of claim 1 wherein the overhang is along all four edges of the attached chip.
5. The device of claim 1 further including terminals surrounding the assembly pad, wherein the attached chip is connected to respective terminals by bonding wires.
6. The device of claim 5 wherein the assembly pad and the terminals are parts of a metal leadframe.
7. The device of claim 5 wherein the assembly pad and the terminals are metal layers and are integral to a laminated substrate.
8. The device of claim 5 further including a package encapsulating the chip, the bonding wires, and at least portions of the assembly pad and terminals.
9. A semiconductor device comprising:
- a first semiconductor chip having an electrically active side and an opposite electrically inactive side, the active side bordered by an edge having a first length, the inactive side bordered by a parallel edge having a second length smaller than the first length;
- a second semiconductor chip having an electrically active side and an opposite electrically inactive side, the active side bordered by an edge having a third length equal to, smaller than, or greater than the first length, the inactive side bordered by a parallel edge having a fourth length smaller than the third length;
- the inactive chip side of the first chip attached to the active side of the second chip so that the edge of the first length is parallel to the edge of the third length;
- an assembly pad having a top side bordered by an edge with a fifth length equal to or smaller than the third length; and
- the inactive chip side of the second chip attached to the top pad side so that the edge of the third length is parallel to the edge of the fifth length, wherein the chips are assembled as a stack on the pad.
10. The device of claim 9 wherein the third length is equal to or smaller than the first length and the active side of the attached first chip forms an overhang over the active side of the second chip.
11. The device of claim 9 wherein the fifth length is smaller than the third length and the active side of the attached second chip forms an overhang over the top pad side.
12. The device of claim 9 further including terminals surrounding the assembly pad, wherein the attached chips are connected to respective terminals by bonding wires.
13. The device of claim 12 wherein the assembly pad and the terminals are parts of a metal leadframe.
14. The device of claim 12 wherein the assembly pad and the terminals are metal layers and are integral to a laminated substrate.
15. The device of claim 12 further including a package encapsulating the chips, the bonding wires, and at least portions of the assembly pad and terminals.
16. A method for fabricating a semiconductor chip comprising:
- providing a semiconductor wafer of a first thickness having an electrically active side and an opposite electrically inactive side, the wafer including a plurality of device chips having linear borders between adjacent chips;
- backgrinding the inactive wafer side to reduce the first wafer thickness to a smaller second thickness;
- forming on the inactive wafer side a grid of linear grooves arrayed in parallel rows intersecting with parallel columns, the rows and columns at right angle to each other, the grooves having edges spaced by a first width and a depth smaller than the second thickness; and
- forming on the active wafer side a matching grid of linear slits arrayed in parallel rows intersecting with parallel columns, the slits having edges spaced by a second width smaller than the first width and a depth merging with respective grooves, wherein merged slits and grooves form cuts singulating discrete rectangular chips from the wafer.
17. The method of claim 16, wherein each singulated chip has an electrically active side bordered by an edge having a first length, and an opposite electrically inactive side bordered by a parallel edge having a second length smaller than the first length.
18. The method of claim 17 wherein the active side forms an overhang over the inactive side.
19. The method of claim 16 wherein the technique to form the grooves is selected from a group including laser saw, mechanical saw with wide blade, chemical etchant, and liquid jet.
20. The method of claim 16 wherein the technique to form the slits is a mechanical saw with thin blade.
21. A method for fabricating a semiconductor device comprising:
- providing a semiconductor chip having an electrically active side and an opposite electrically inactive side, the active side bordered by an edge having a first length, the inactive side bordered by a parallel edge having a second length smaller than the first length;
- providing a substrate having an assembly pad bordered by a linear edge having a third length smaller than the first length; and
- attaching the inactive chip side to the pad.
22. The method of claim 21 wherein the substrate further includes terminals surrounding the assembly pad.
23. The method of claim 22 further including the processes of:
- connecting the chip to respective substrate terminals by bonding wires; and
- encapsulating the chip and bonding wires in a packaging compound.
24. A method for fabricating a semiconductor device comprising:
- providing a first semiconductor chip having an electrically active side and an opposite electrically inactive side, the active side bordered by an edge having a first length, the inactive side bordered by a parallel edge having a second length smaller than the first length;
- providing a second semiconductor chip having an electrically active side and an opposite electrically inactive side, the active side bordered by an edge having a third length equal to, smaller, or greater than the first length, the inactive side bordered by a parallel edge having a fourth length smaller than the third length;
- attaching the inactive chip side of the first chip to the active side of the second chip so that the edge of the first length is parallel to the edge of the third length;
- providing a substrate having an assembly pad bordered by a linear edge with a fifth length equal to or smaller than the third length; and
- attaching the inactive chip side of the second chip to the pad so that the edge of the third length is parallel to the edge of the fifth length.
25. The method of claim 24 wherein the third length is equal to or smaller than the first length and the active side of the attached first chip forms an overhang over the active side of the second chip.
26. The method of claim 24 wherein the fifth length is smaller than the third length and the active side of the attached second chip forms an overhang over the pad.
27. The method of claim 24 wherein the substrate further includes terminals surrounding the assembly pad.
28. The method of claim 27 further including the processes of:
- connecting the chips to respective substrate terminals by bonding wires; and
- encapsulating the chips and bonding wires in a packaging compound.
Type: Application
Filed: Dec 23, 2014
Publication Date: Jun 23, 2016
Inventors: Alok Kumar Lohia (Dallas, TX), Reynaldo Corpuz Javier (Plano, TX), Andy Quang Tran (Grand Prairie, TX)
Application Number: 14/580,836