Micro-electro-mechanical system having movable element integrated into leadframe-based package
A MEMS may integrate movable MEMS parts, such as mechanical elements, flexible membranes, and sensors, with the low-cost device package, leaving the electronics and signal-processing parts in the integrated circuitry of the semiconductor chip. The package may be a leadframe-based plastic molded body having an opening through the thickness of the body. The movable part may be anchored in the body and extend at least partially across the opening. The chip may be flip-assembled to the leads to span across the foil, and may be separated from the foil by a gap. The leadframe may be a prefabricated piece part, or may be fabricated in a process flow with metal deposition on a sacrificial carrier and patterning of the metal layer. The resulting leadframe may be flat or may have an offset structure useful for stacked package-on-package devices.
1. A method for fabricating a microelectromechanical system (MEMS) device, comprising:
providing a leadframe having a first surface, the leadframe defining a plurality of leads and a segment;
depositing a polymeric compound over the leadframe first surface including at the leads and a peripheral portion of the segment, leaving the first surface at another portion of the segment unencapsulated at a bottom of an opening through the polymeric compound, the unencapsulated portion defining a movable part of the MEMS device; and
connecting a semiconductor chip having electronic circuitry on a first chip surface at the leads to a second surface of the leadframe, so that the first chip surface spans across the movable part, separated from the movable part by a gap.
2. The method of claim 1 , wherein the leadframe is provided in the form of a patterned metal sheet.
3. The method of claim 2 , further comprising thinning a thickness of the segment at the unencapsulated portion after depositing the polymeric compound.
4. The method of claim 3 , wherein the leads comprise first and second leads; the semiconductor chip is connected at the first leads; and solder balls are attached to the second leads for connection to external parts.
5. The method of claim 1 , further comprising thinning a thickness of the segment at the unencapsulated portion after depositing the polymeric compound.
6. The method of claim 1 , wherein providing the leadframe includes depositing a metal layer onto a carrier and patterning the metal layer to define the leads and the segment; and the method further comprises removing the carrier from the patterned metal layer after depositing the polymeric compound and before connecting the semiconductor chip.
7. A method for fabricating a microelectromechanical system (MEMS) device, comprising:
providing a leadframe having first and second surfaces, the leadframe defining a plurality of leads and a segment;
encapsulating the second leadframe surface in a polymeric compound of a thickness, leaving a portion of the second leadframe surface at the segment unencapsulated at an opening through the thickness;
thinning the segment at the location of the unencapsulated portion to define a foil suitable as a movable part of the MEMS device; and
connecting a semiconductor chip having electronic circuitry on a first chip surface to the leads at the first leadframe surface so that the first chip surface with the electronic circuitry faces and spans the foil, separated from the foil by a gap.
8. The method of claim 7 , further comprising forming a solderable metallurgical configuration on the first leadframe surface.
9. The method of claim 7 , wherein the leadframe is provided as a preformed planar metal part.
10. The method of claim 7 , further comprising configuring the leadframe to provide the segment and first ones of the leads in a first plane, and second ones of the leads in a second plane offset from the first plane.
11. The method of claim 7 , further comprising hardening the deposited polymeric compound by polymerization.
12. The method of claim 7 , wherein the circuitry of the chip includes a metal plate; and connecting the chip includes aligning the metal plate with the leadframe segment.