This disclosure relates generally to flip chip mounted MMIC structures.
As is known in the art, Monolithic microwave integrated circuit (“MMIC”) chips are often mounted on a printed circuit board (PCB) by metal or solder posts (sometimes referred to as bonding posts or bumps) to form a MMIC chip system. When a MMIC chip is mounted with the circuits facing the circuit board, it is referred to as a “MMIC flip chip system.” The difference in thermal expansion properties between the MMIC flip chip and the circuit board can create mechanical stresses on the metal or solder posts when the system experiences temperature cycles or large thermal fluctuations. These stresses may render the system unreliable.
A conventional solution is to insert a dielectric underfill material (e.g., an adhesive) having desirable mechanical properties between the MMIC flip chip and the circuit board to reduce the stresses on the metal or solder posts. However, due to undesirable dielectric properties, underfill contacting sensitive components of the MMIC flip chip can degrade the electrical performance of the chip.
Prior solutions to this problem include using tall metal or solder posts that provide sufficient flexibility during thermal expansion to alleviate the need for underfill. Another approach is to apply underfill carefully to avoid the sensitive components of the MMIC flip chip. Both of these approaches require non-standard processes and are therefore unavailable or expensive to implement.
In accordance with the present disclosure, a MMIC flip chip mounted to a circuit board is provided having an underfill material disposed between the MMIC and the circuit board and a barrier structure for preventing the underfill material from being disposed under an electronic device of the MMIC while providing a cavity under the electronic device.
In one embodiment, the barrier structure is disposed on the circuit board.
In one embodiment, the barrier structure is disposed on the MMIC.
In one embodiment, the barrier structure comprises one or more dam like structures.
In one embodiment, the barrier structure is a tub like structure.
In one embodiment, a structure is provided comprising: a MMIC having an electronic device; a circuit board having the MMIC flip chip mounted to the circuit board; an underfill material disposed between the MMIC and the circuit board; and a barrier structure for preventing the underfill material from being disposed under the active device while providing a cavity under the electronic device.
In one embodiment, the printed circuit board has an electronic device contact pad and wherein the electronic device contact pad is electrically connected to the electronic device.
In one embodiment, the underfill material is an adhesive.
In one embodiment, bonding posts are disposed between the printed circuit board and the MMIC and wherein the underfill material reduces mechanical stresses on the bonding posts.
In one embodiment, a structure is provided comprising: a MMIC having an electronic device; a circuit board having the MMIC flip chip mounted to the circuit board; an underfill material disposed between the MMIC and the circuit board; and a barrier structure for preventing the underfill material from being disposed under the electronic device while providing an gaseous filled region under the electronic device.
In one embodiment the printed circuit board has an active device contact pad and wherein the electronic device contact pad is electrically connected to the electronic device.
In one embodiment a structure is provided having: a MMIC having an electronic device disposed in a front surface of thereof; a printed circuit board; wherein the MMIC is flip-chip mounted to the printed circuit; an underfill material deposed between the printed circuit board and the front surface of the flip chip mounted MMIC; and a barrier structure for preventing the underfill material from being disposed under the device while providing an gaseous filled region within the barrier structure under the electronic device of the flip chip mounted MMIC.
In one embodiment, the structure includes bonding posts disposed between the printed circuit board and the MMIC and wherein the underfill material reduces mechanical stresses on the posts.
In one embodiment, the barrier structure creates a capillary between the flip chip mounted MMIC and the printed circuit board to direct the flow of underfill material away from the region under the electronic device.
In one embodiment, the barrier structure creates a capillary between the flip chip mounted MMIC and the printed circuit board to direct the flow of underfill away from the region under the electronic device and create a gas bubble in the region under the electronic device.
In one embodiment, the bonding posts comprise a metal and a solder on the metal wherein the metal post has a higher melting point that the solder and wherein when heated attaches the MMIC to the printed circuit board at a proper spacing there between to enable the barrier structure to prevent the underfill material from being disposed in a region under the electronic device.
The details of one or more embodiments of the disclosure are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the disclosure will be apparent from the description and drawings, and from the claims.
Like reference symbols in the various drawings indicate like elements.
Referring now to
The structure 10 (
More particularly, a dielectric layer 32, here for example, Benzocyclobutene (BCB), is photolithographically formed over the front surface 16 of the MMIC chip 12 and patterned to have an opening therein 33 over the electronic device 14. It is noted that the upper surface 35 of the sidewalls 23 are in contact with the BCB 32 to prevent the underfill material 20 from passing into the cavity 21 of the barrier structure 22. It is further noted that the contact between the barrier structure 22 and the BCB 32 does not have to form a perfect seal in order to prevent the underfill material 20 from passing into the cavity 21 of the barrier structure 22, due to capillary between the flip chip mounted MMIC and the printed circuit board and gas pressure effects created by the overall structure 10 to be described below in connection with
The printed circuit board 18 (
It should be understood that some of the contact pads may not be directly connected to the electronic device. For example, they may be connected to matching networks, etc., (not shown) between the pads and the electronic devices.
As will be described in more detail below, the barrier structure 22 creates a capillary in the gap between the flip chip mounted MMIC chip 12 and the printed circuit board 18 to direct the flow of underfill material 20 away from the region 24 under the electronic device 14 and create a gas, for example air or nitrogen, bubble in the region 24 under the electronic device 12.
Referring now to
The MMIC 12 (
Here, the active device 14 is a FET having: a plurality of finger-like gate electrodes G connected to a gate contacts G, a plurality of source electrodes S electrically interconnected together by an air-bridge conductor 66, and drain electrodes D disposed under the air bridge conductor 66 connected to the CPW transmission lines.
As noted above, the microwave structure 10 includes a multilayer printed circuit board 18 (
Referring now to
Next, referring to
More particularly, the metal 48 of the post 44 has a higher melting point that the solder 46 of the post 44 so that when heated the post 44 attaches the MMIC 12 to the printed circuit board 18 at a proper spacing there between to enable the barrier structure 22 to prevent the underfill material 20, to be added, from flowing into the region 24 under the active device 14 (more particularly into the cavity 21 in the barrier structure 22.
Next, after the MMIC chip 12 is bonded to the printed circuit board 18, as shown in
A number of embodiments of the disclosure have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the disclosure. For example, while in the description above, the barrier structure 22 is disposed on the circuit board 12, the barrier structure 22′ having sidewalls 23′ may be disposed about the MMIC 12 as shown in
Number | Name | Date | Kind |
---|---|---|---|
5524339 | Gorowitz et al. | Jun 1996 | A |
5757072 | Gorowitz et al. | May 1998 | A |
5977631 | Notani | Nov 1999 | A |
6118357 | Tomasevic et al. | Sep 2000 | A |
6124636 | Kusamitsu | Sep 2000 | A |
6495915 | Hsieh et al. | Dec 2002 | B1 |
7631414 | Quil et al. | Dec 2009 | B2 |
8039957 | Heinrich et al. | Oct 2011 | B2 |
20030189246 | Iwaki et al. | Oct 2003 | A1 |
20050104204 | Kawakubo et al. | May 2005 | A1 |
20060211233 | Gan et al. | Sep 2006 | A1 |
20080064142 | Gan et al. | Mar 2008 | A1 |
20080308922 | Zhang et al. | Dec 2008 | A1 |
20100013088 | Davis et al. | Jan 2010 | A1 |
20130075795 | Hauhe et al. | Mar 2013 | A1 |
Entry |
---|
U.S. Appl. No. 13/200,477, filed Sep. 23, 2011, entitled Aerogel Dielectric Layer, pp. 1-21. |
U.S. Appl. No. 13/331,408, filed Dec. 20, 2011, entitled Method for Packaging Semiconductors at a Wafer Level, pp. 1-15. |
G. Baumann, E. Willer, F. Buchali, D. Ferling, H. Ritcher, W. Heinrich, Evaluation of Glob Top and Underfill Encapsulated Active and Passive Structures for Millimeter Wave Application, pp. 26-31. |