Patent Application
20080087979
Those skilled in the art should more fully appreciate advantages of various embodiments of the invention from the following “Description of Illustrative Embodiments,” discussed with reference to the drawings summarized immediately below.
In illustrative embodiments of the invention, an integrated circuit has a conductive path that effectively extends from its front side, through its substrate and across its back side. Such a topology more efficiently enables multiple chips to be mounted in a stacked configuration, consequently reducing space requirements of an underlying circuit board or similar circuit mounting apparatus. Details illustrative embodiments are discussed below.
To that end, the system 10 has a circuit board 14 supporting and selectively interconnecting a plurality of different electronic components. Among other things, the components can include analog circuits, digital circuits, integrated circuits, and discrete components. As shown, the circuit board 14 has three integrated circuits 12 and another circuit element 13 (e.g., a capacitor). Two of the integrated circuits 12 are configured in accordance with illustrative embodiments of invention.
Specifically, as discussed below, the two integrated circuits 12 configured in accordance with illustrative embodiments each have a conductive path 16 extending between the front and back sides 22 and 24 of their respective substrates 26 (see
The integrated circuits 12 shown in
The integrated circuits 12 may implement other types of MEMS devices or other circuit functionality. For example, the integrated circuits 12 may implement a MEMS microphone or pressure sensor. As yet another example, the integrated circuits 12 may implement conventional circuit functionality, such as an operational amplifier, an analog-to-digital converter, and/or a microprocessor.
In a similar manner, a conventional package may contain and protect the MEMS device, which itself may be in a flip-chip or non-flip chip configuration. Accordingly, discussion of the type of device on the integrated circuit 12 and specific packaging is illustrative and not intended to limit various embodiments of the invention.
As shown in
Conductive traces 18 on the back side 24 electrically connect together selected contact pads 20. For example, the integrated circuit 12 shown in
Of course, those skilled in the art can form conductive traces 18 or other similar interconnecting conductors on the back side 24 of the substrate 26 in any configuration as required by the intended application. To that end, a circuit designer may electrically connect certain contact pads 20 based upon the corresponding land configuration of the integrated circuit 12 that is to be mounted on its back side 24. Alternatively, a circuit designer may electrically connect certain contact pads 20 to provide flexibility for integrated circuits 12 having a variety of different corresponding land configurations. For example, a circuit designer may connect specific pads 20 so that it readily connects with integrated circuits 12 having two different land patterns. Accordingly, the configuration shown in
Interconnects 30 on the front side 22 electrically connect the working portion 28 with one or more of the conductive paths 16. These conductive paths 16 may terminate at a first type of contact pad 20. Specifically, the first type of contact pad 20 is directly connected to the conductive path terminus point on the back side 24 (i.e., effectively forming part of the conductive path 16). Moreover, conductive traces 18 on the back side 24 may connect the conductive paths 16 with contact pads 20 that are not directly connected with the conductive paths 16. This second type of contact pad 20 may be formed by depositing metal on a back side surface that is not the terminus of a conductive path 16. For example, as discussed below, this type of contact pad 20 may have been formed on an insulator that is deposited on the back side surface. Such pad 20 has no direct connection to the conductive path 16 through the substrate 26. Accordingly, the working portion 28 can forward and/or receive an electronic signal via a complete transmission line comprising the following links:
The front side 22 of the of the substrate 26 also has a plurality of mechanical contacts 32 for electrical and mechanically connecting with another apparatus. Among other things, the mechanical contacts 32 may be one or more conventional solder balls (also referred to as “solder balls 32”). Each solder ball 32 directly connects to the conductive path 16 through the substrate 26. Alternatively, one or more of the solder balls 32 may not directly contact one of the conductive paths 16 through the substrate 26.
The bottom integrated circuit 12 is configured in accordance with illustrative embodiments of the invention. The conductive paths 16 through the bottom integrated circuit 12 are shown as extending straight through the substrate 26 with a substantially uniformly changing diameter. However, some embodiments of the conductive path 16 have a substantially uniform diameter, irregular shape, irregular outer dimension, and/or do not extend straight through the substrate 26. For example, the conductive paths 16 may extend somewhat diagonally through the substrate 26. Discussion of one type of conductive path 16 therefore is illustrative and not intended to limit the number of embodiments of the invention.
In some embodiments, the top integrated circuit 12 in
The process begins at step 400 by forming a working portion 28 on a wafer, e.g., a single crystal silicon wafer, in a conventional manner. As noted above, the working portion 28 can have circuitry, MEMS structure, or both. If necessary, the working portion 28 may be capped, or otherwise protected at this or some later point in the process (e.g., see step 408, which discusses passivation).
The process continues to step 402, where the working portion 28 is tested to ensure that it works satisfactorily for its intended purpose. At this point, a fully functional device may be considered to be formed. This device, however, also requires some additional interconnect apparatus to connect with other devices, such as other integrated circuits 12 through the circuit board 14 as shown in
Accordingly, the process forms one or more conductive paths 16 to communicate with other devices. To that end, step 404 of the process forms a channel from the substrate front side 22 (i.e., the side having the working portion 28) to the substrate back side 24. This channel may be referred to in the art as a “via.”
After forming the channel through the substrate 26, the process continues to step 406, which adds conductive material to the channel to form the conductive path 16 through the substrate 26. In some embodiments, the conductive material may fill the entire channel. In other embodiments, the conductive material coats at least a portion of the wall(s) of the channel. In either case, the conductive path 16 is considered to be integrated with the substrate 26. Among other things, the conductive material may be a metal or doped polysilicon. For interconnection purposes, the terminus portion of each conductive path 16 may be considered to effectively form a “front side contact.” Alternatively, an additional step may add a front side contact of like or different material. The process thus may form the interconnects 30 between the front side contacts and working portion 28 at this time.
Rather than directly adding the conductive material to the channel, some embodiments add an insulator to the channel walls to electrically isolate the conductive path 16 from the substrate 26. As an example, the insulator may be an oxide that is grown or deposited in accordance with conventional processes. After applying the insulator 16 to the wall(s), the conductive material is added.
The process continues to step 408, which forms the back side electrical connections. Specifically, the process deposits connector material to form the contact pads 20 and conductive traces 18. In a manner similar to the conductive paths 16 through the substrate 26, the contact pads 20 and conductive traces 18 are considered to be integrated with the substrate 26. These electrical connections may be formed by first applying an insulator to a portion of the back side 24, and then forming the conductive traces 18 on the insulator. Among other ways, illustrative embodiments may apply the conductive material to the insulator layer by means of a conventional sputtered metal process, or an electroplating process. Another layer of insulator also may be deposited on the back side 24, front side 22, or both, to collectively insulate the exposed portions of the conductive traces 18 and interconnects 30. This insulation process, which often is referred to in the art as “passivation,” may use any number of materials, such as a nitride or polyimide.
Accordingly, the conductive traces 18 may be considered to be on the back side 24 of the substrate 26 even if covered by some other material. As another example, some embodiments may etch trenches in the surface of the back side 24, insulate the trenches with an oxide, and then deposit a doped polysilicon or metal into the insulated trenches. Additional passivation may then cover the conductive traces 18, or other layers may be formed over the trenches.
The process concludes at step 410 by depositing the solder balls 32 on the front side 22 of the substrate 26. The solder balls 32 may be any conventional solder material, such as a conventional SAC solder, which includes tin, silver, and copper. Solder balls 32 directly connected to the conductive paths 16 may be considered to be part of the front side contacts.
At this point, the integrated circuit 12 may be packaged within a conventional package, or secured directly to a printed circuit board 14, as shown in
It should be noted that the process of
Moreover, some of the steps in the process may be executed in an order that is different than that discussed above. For example, the working portion 28 may be formed after forming the conductive path 16 through the substrate 26. Accordingly, discussion of the process of
By extending the conductive path 16 through the substrate 26, the conductive traces 18 on the back side 24 efficiently distribute electrical signals to and from the working portion 28 to multiple contact pads 20. Accordingly, illustrative embodiments efficiently enable integrated circuits 12 to be connected in a stacked configuration.
Although the above discussion discloses various exemplary embodiments of the invention, it should be apparent that those skilled in the art can make various modifications that will achieve some of the advantages of the invention without departing from the true scope of the invention.
