Method of fabricating a molded package for micromechanical devices

• US 20030045025A1
• Filed: 10/16/2002
• Published: 03/06/2003
• Est. Priority Date: 01/26/2000
• Status: Active Grant

• Current Assignee: Anthony L. Coyle, George A. Bednarz
• Original Assignee: Anthony L. Coyle, George A. Bednarz
• Inventors: Coyle, Anthony L., Bednarz, George A.
• Granted Patent: US 6,858,910 B2
• Time in Patent Office: Days
• US Class Current: 438/106
• CPC Class Codes: B29C 2045/14663 the mould cavity walls being lined with a film, e.g. release film
• CPC Class Codes: B29C 45/14655 connected to or mounted on a carrier, e.g. lead frame
• CPC Class Codes: B81C 1/00333 Aspects relating to packaging of MEMS devices, not covered by groups B81C1/00269 - B81C1/00325
• CPC Class Codes: B81C 2203/0154 Moulding a cap over the MEMS device
• CPC Class Codes: H01L 21/565 Moulds
• CPC Class Codes: H01L 2224/05568 the whole external layer protruding from the surface
• CPC Class Codes: H01L 2224/05573 Single external layer
• CPC Class Codes: H01L 2224/05599 Material
• CPC Class Codes: H01L 2224/05624 Aluminium [Al] as principal constituent
• CPC Class Codes: H01L 2224/05647 Copper [Cu] as principal constituent
• CPC Class Codes: H01L 2224/16245 the item being metallic
• CPC Class Codes: H01L 2224/45014 Ribbon connectors, e.g. rectangular cross-section
• CPC Class Codes: H01L 2224/45015 being circular
• CPC Class Codes: H01L 2224/45124 Aluminium (Al) as principal constituent
• CPC Class Codes: H01L 2224/45144 Gold (Au) as principal constituent
• CPC Class Codes: H01L 2224/45147 Copper (Cu) as principal constituent
• CPC Class Codes: H01L 2224/48091 Arched
• CPC Class Codes: H01L 2224/48227 connecting the wire to a bond pad of the item
• CPC Class Codes: H01L 23/3107 the device being completely enclosed
• CPC Class Codes: H01L 24/45 of an individual wire connector
• CPC Class Codes: H01L 24/48 : of an individual wire connector
• CPC Class Codes: H01L 2924/00 : Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
• CPC Class Codes: H01L 2924/00012 : Relevant to the scope of the group, the symbol of which is combined with the symbol of this group
• CPC Class Codes: H01L 2924/00013 : Fully indexed content
• CPC Class Codes: H01L 2924/00014 : the subject-matter covered by the group, the symbol of which is combined with the symbol of this group, being disclosed without further technical details
• CPC Class Codes: H01L 2924/01004 : Beryllium [Be]
• CPC Class Codes: H01L 2924/01015 : Phosphorus [P]
• CPC Class Codes: H01L 2924/01046 : Palladium [Pd]
• CPC Class Codes: H01L 2924/01047 : Silver [Ag]
• CPC Class Codes: H01L 2924/01078 : Platinum [Pt]
• CPC Class Codes: H01L 2924/01079 : Gold [Au]
• CPC Class Codes: H01L 2924/01087 : Francium [Fr]
• CPC Class Codes: H01L 2924/013 : Alloys
• CPC Class Codes: H01L 2924/01327 : Intermediate phases, i.e. intermetallics compounds
• CPC Class Codes: H01L 2924/10253 : Silicon [Si]
• CPC Class Codes: H01L 2924/12042 : LASER
• CPC Class Codes: H01L 2924/14 : Integrated circuits
• CPC Class Codes: H01L 2924/15311 : being a ball array, e.g. BGA
• CPC Class Codes: H01L 2924/15747 : Copper [Cu] as principal constituent
• CPC Class Codes: H01L 2924/181 : Encapsulation
• CPC Class Codes: H01L 2924/1815 : Shape
• CPC Class Codes: H01L 2924/206 : Length ranges
• CPC Class Codes: H01L 2924/20751 : larger or equal to 10 microns less than 20 microns
• CPC Class Codes: H01L 2924/20752 : larger or equal to 20 microns less than 30 microns
• CPC Class Codes: H01L 2924/20753 : larger or equal to 30 microns less than 40 microns

Abstract

A plastic land-grid array package, a ball-grid array package, and a plastic leaded package or micromechanical components are fabricated by a molding process characterized by lining the cavity surfaces of the top and bottom mold halves with a protective plastic film, which also protects the surfaces or the components during the molding phase, selectively encapsulating the bonding pads and coupling members of the chip while leaving empty space above the components, and attaching a lid over the components A molding method as well as a molding apparatus are provided compatible with the sensitivity of the micromechanical devices, yet flexible with regard to the technique used to assemble the chip and the substrate. Furthermore, the method disclosed is flexible with regard to the material and the properties of the substrate.

It is an aspect of the present invention to be applicable to a variety of different semiconductor micromechanical devices, for instance actuators, motors, sensors, spatial light modulators, and deformable mirror devices. In all applications, the invention achieves technical advantages as well as significant cost reduction and yield increase.

Claims

1. A method of fabricating a molded device by encapsulating a semiconductor chip having an integrated circuit including a plurality of micromechanical components, configured in a plane in the central area of said chip, and a plurality of bonding pads, disposed in peripheral areas of said chip, comprising the steps of:

forming an electrically insulating substrate, having a plurality of conductive routing lines, first and second surfaces, and a plurality or terminals on said second surface, said terminals electrically connected with said routing lines, respectively;

assembling said chip onto said first substrate surface;

providing a mold for encapsulating said assembled chip, said mold having top and bottom halves;

lining said top and bottom halves with a protective plastic film;

loading said substrate including said assembled chip into said mold;

introducing an encapsulation material into said mold;

curing said encapsulation material at least partially, thereby forming a molded frame around said chip, while leaving empty space above said components, said frame having a flat surface in a plane parallel to said plane of said components;

removing said substrate together with said encapsulated chip from said mold;

attaching a lid to said flat surface of said molded frame, thereby positioning said lid in a plane parallel to said plane of said components; and

attaching an array of solder balls to said substrate terminals.

2. The method according to claim 1 wherein said steps of assembling, providing, loading and introducing comprise the steps of:

attaching said chip onto said first surface of said substrate;

electrically connecting said chip bonding pads to said substrate routing lines, using coupling members;

forming a mold having top and bottom halves each having a cavity for holding said assembled chip, said top half providing a central flat portion having the outline and area equal to the outline and area of said plurality of components, said mold further having gates and runners for feeding encapsulation material into said cavities;

positioning said substrate together with said assembled chip into said bottom mold half, thereby positioning said components away from said bottom mold half;

closing said mold by clamping said too half onto said bottom half, whereby said film uniformly contracts said components, forming a tight seal with the surfaces of said components; and

pressuring encapsulation material through said runners and gates into said cavities, thereby depositing flowable encapsulation material on said peripheral areas of said assembled chip, engulfing and protecting said coupling members and bonding pads, while leaving empty space above said components.

3. The method according to claim 1 wherein said micromechanical components are micromirrors.

4. The method according to claim 1 wherein said insulating substrate is selected from a group consisting of flexible films made of polymers, polyimides or epoxies, and sheet-like boards made of FR-4, F-5, BT resin, or glass-fiber strengthened dielectrics.

5. The method according to claim 2 wherein said coupling members are selected from a group consisting of bonding wires, bonding ribbons, solder balls, or solder bumps.

6. The method according to claim 2 wherein said step of electrically connecting is performed by moving the bonding tool the shortest feasible distance over the surface of said substrate, thereby spacing a minimum length of coupling members.

7. The method according to claim 1 wherein said encapsulation material is selected from a group consisting of epoxy-based thermoset resins, silicone-based elastomerics, and low viscosity molding compounds filled with a silica and anhydrides and formulated for high adhesion.

8. The method according to claim 2 wherein said too mold half further provides a portion intended for forming ridge-like molded protrusions positioned under said lid and suitable for storing chemical compounds.

9. The method according to claim 1 further comprising the step of depositing chemical compounds before attaching said lid to said molded frame.

10. The method according to claim 9 wherein said chemical compound is a pill or a granular material suitable for releasing passivants continuously to coat contacting surfaces of said components.

11. The method according to claim 1 wherein said lid is a plate made of glass or any other material transparent to light in the visible range of the electromagnetic spectrum.

12. The method according to claim 1 wherein said lid is attached to said flat frame surface by an epoxy adhesive.

13. The method according to claim 1 wherein said chip has outline and said substrate has an outline substantially the same as said outline of said chip.

14. The method according to claim 13 further comprising the step of trimming said molded device, thereby forming a device having an outline substantially the same as said outline of said chip.

15. A method of fabricating a molded device by encapsulating a semiconductor chip having an integrated circuit including a plurality of micromechanical components, configured in a plane in the central area of said chip, and a plurality of bonding pads, disposed in peripheral areas of said chip, comprising the steps of:

forming a leadframe, having a chip mount pad for an integrated circuit chip and a plurality of lead segments, each segment having a first end near said mount pad and a second end remote from said mount pad;

assembling said chip onto said mount pad;

providing a mold for encapsulating said assembled chip, said mold having top and bottom halves;

lining said top and bottom halves with a protective plastic film;

loading said leadframe including said assembled chip into said mold;

introducing an encapsulation material into said mold;

curing said encapsulation material at least partially, thereby forming a molded frame around said chip, while leaving empty space above said components, said frame having a flat surface in a plane parallel to said plane of said components;

removing said substrate together with said encapsulated chip from said mold;

attaching a lid to said flat surface of said molded frame, thereby positioning said lid in a plane parallel to said plane of said components; and

trimming and forming said second segment ends of said leadframe.

16. The method according to claim 15 wherein said steps of assembling, providing, loading and introducing comprise-the steps of:

attaching said chip onto said mount pad of said leadframe;

electrically connecting said chip bonding pads to said first segment ends, using coupling members;

forming a mold having top and bottom halves each having a cavity for holding said assembled chip, said too half providing a central flat portion having the outline and area equal to the outline and area of said plurality of components, said mold further having gates and runners for feeding encapsulation material into said cavities;

positioning said leadframe together with said assembled chip into said bottom mold half, thereby positioning said components away from said bottom mold half;

closing said mold by clamping said top half onto said bottom half, whereby said film uniformly contacts said components, forming a tight seal with the surfaces of said components; and

pressuring encapsulation material through said runners and gates into said cavities, thereby depositing flowable encapsulation material on said peripheral areas of said assembled chip, engulfing and protecting said coupling members and bonding pads, while leaving empty space above said components.

17. An apparatus for molding the encapsulation or a semiconductor chip having an integrated circuit including a plurality of micromechanical components, configured in a plane in the central area of said chip, and a plurality of bonding pads, disposed in peripheral areas of said chip, said chip pre-assembled on a substrate by coupling members, comprising:

a mold having top and bottom halves each having a cavity for holding said pre-assembled chip;

said top half providing a central flat portion having the outline and area equal to the outline and area of said plurality of components;

said top half further providing peripheral flat portions having the outline and at least the areas of said plurality of bonding pads combined with the areas required by said coupling members;

said top and bottom cavities lined with protective plastic films;

said top half operable to position said central and peripheral flat portions in planes parallel to said plane or said components, whereby said film over said central flat portion uniformly contacts said components; and

one of said halves having a plurality of runners and a plurality of gates for feeding encapsulation material into said cavities.

18. The apparatus according to claim 17 wherein said top half of said mold is further configured to create ridge-like molded protrusions suitable for storing chemical compounds.