This application claims priority from U.S. patent application 61/870,354, filed Aug. 27, 2013. Priority is claimed to this earlier filed application and the contents of this earlier-filed application are incorporated herein, in their entirety, by reference.
The present invention relates generally to integrated circuits, and more particularly to a cavity package with a pre-molded cavity leadframe.
Flat no-leads packages such as QFN (quad-flat no-leads) and DFN (dual-flat no-leads) are used to physically and electrically connect integrated circuits to printed circuit boards. Two types of flat no-leads packages are common: cavity (i.e. with a cavity designed into the package containing air or nitrogen), and plastic-molded (i.e. with minimal air in the package). The cavity package is usually made up of three parts; a copper leadframe, plastic-molded body (open, and not sealed), and a cap or lid attached to the plastic portion of the leadframe. An integrated circuit (IC) is mounted to a die attach pad within the cavity, with wire leads connecting the IC to the leadframe. The leadframe terminates in contacts on the bottom of the package for providing electrical interconnection with a printed circuit board.
Cavity packages are small and lightweight, with good thermal and electrical performance that makes them suitable for portable communication/consumer products. Applications include cellular phones, PDAs, wireless transmitters, RF front end, HD devices, microcontrollers, pre-amplifiers, servers, smart power suppliers, switches, DSPs, ASICs and wrist watches.
According to an aspect of the invention, a metal ring is integrated into the pre-molded cavity leadframe. The metal ring provides an electrical ground path from the metal cap to the die attach pad and permits attachment of the metal cap to the pre-molded leadframe using solder reflow onto.
Features and advantages of the invention will be apparent from the detailed description which follows, taken in conjunction with the accompanying drawings, which together illustrate, by way of example, features of the invention; and, wherein:
Reference will now be made to the exemplary embodiments illustrated, and specific language will be used herein to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended.
Before the present invention is disclosed and described, it is to be understood that this invention is not limited to the particular structures, process steps, or materials disclosed herein, but is extended to equivalents thereof as would be recognized by those ordinarily skilled in the relevant arts. It should also be understood that terminology employed herein is used for the purpose of describing particular embodiments only and is not intended to be limiting.
With reference to
As discussed above, and as shown in
Construction of the cavity package involves a two-part process beginning with pre-mold cavity leadframe fabrication, followed by assembly, as shown in
The pre-mold cavity leadframe fabrication begins at step 100 (
At step 110, the supporting and connecting leads 510 are shaped by mechanical bending, for example using a punch tool and anvil block, so that the matrix of rings ‘stands’ on leads 510 at an appropriate height above the leadframe 200, as discussed in greater detail below.
At step 120, the leadframe 210 is fabricated in a matrix, as shown in
At step 130, the metal frame of rings 400 is mechanically and electrically connected to the leadframe 210 (e.g. by conductive epoxy, soldering, spot welding, etc.), as shown in
At step 140, leadframe 210 is molded in plastic molded body 220 to form a cavity 1000 for receiving the semiconductor device die in a subsequent step. The top side of the metal ring 400, a portion of the top side of the bonding fingers 420, the top side of the die attach pad 410, the bottom side of the bonding fingers 420 and the bottom side of the die attach pad 410 are all exposed after molding, as shown in
The assembly process begins at step 150, wherein the semiconductor die 1300 is attached to the die attach pad 410 of the pre-molded leadframe 200, followed by wire bonding 1310, as shown in
At step 160, the metal cap 230 is fabricated. Step 160 can be performed before, after or simultaneously with step 150.
At step 170, the cap 230 is attached to the top of the pre-molded cavity leadframe. The cap can be attached using conductive epoxy and solder reflow onto the exposed top surface of the metal seal ring 400 embedded into the pre-molded cavity leadframe. The metal ring 400 provides an electrical ground path from the metal cap 230 to the die attach pad 410 and permits attachment of the metal cap to the pre-molded leadframe using solder reflow.
After the cap 230 has been attached, at step 180, the matrix is singulated (e.g. using saw singulation) to create individual units.
Steps 150, 170 and 180 comprise the assembly process of the overall process of
Referring again to step 130 of
According to a first sub-step of the alternative step 130, the solder ball contact area, the lead tips of each wire bond finger 420, and the periphery of the top surface of the die attach pad 410 on the leadframe 210 are selectively pre-plated by wire bondable and “solderable” metal (e.g. Ni/Au, Ni/Pd/Au, Ag, etc). The bottom exposed metal areas of the leadframe 210 are also selectively plated for surface mount reflow. The remainder of the non plated area of the leadframe 210 is then passivated (e.g. by oxidizing the base metal). Passivation acts as a solder resist for restricting undesired solder wetting. Solder balls 1500 are then placed as shown in
While the forgoing exemplary embodiment is illustrative of the principles of the present invention, it will be apparent to those of ordinary skill in the art that numerous modifications in form, usage and details of implementation can be made without the exercise of inventive faculty, and without departing from the principles and concepts of the invention. Accordingly, it is not intended that the invention be limited, except as by the claims set forth below.
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Number | Date | Country |
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Entry |
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Fan, “Cavity Package with Pre-Molded Cavity LeadFrame”, U.S. Appl. No. 14/446,390, filed Jul. 30, 2014. |
Non-Final Rejection dated Jul. 29, 2016 for U.S. Appl. No. 14/469,811. |
Non-Final Rejection dated Jan. 14, 2016 in Related U.S. Appl. No. 14/469,811. |
Number | Date | Country | |
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20160126164 A1 | May 2016 | US |
Number | Date | Country | |
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61870354 | Aug 2013 | US |
Number | Date | Country | |
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Parent | 14446390 | Jul 2014 | US |
Child | 14993175 | US |