Partially patterned lead frames and methods of making and using the same in semiconductor packaging
View Patent ↗A method of making a lead frame and a partially patterned lead frame package with near-chip scale packaging lead-count, wherein the method lends itself to better automation of the manufacturing line and improved quality and reliability of the packages produced therefrom. A major portion of the manufacturing process steps is performed with a partially patterned strip of metal formed into a web-like lead frame on one side so that the web-like lead frame is also rigid mechanically and robust thermally to perform without distortion or deformation during the chip-attach and wire bond processes, both at the chip level and the package level. The bottom side of the metal lead frame is patterned to isolate the chip-pad and the wire bond contacts only after the front side, including the chip and wires, is hermetically sealed with an encapsulant. The resultant package being electrically isolated enables strip testing and reliable singulation.
1. A method of forming electronic packages, the method comprising the steps of:
forming a block of partially etched lead frames having selectively pre-plated top and bottom surfaces, the lead frames comprising webbed portions, chip attachment areas, and electrical lead portions in the form of pull-in leads, wherein the electrical lead portions are electrically separated from the chip attachment areas, and the lead frames are separated from each other by street portions;
attaching a chip to a corresponding chip attachment area of a lead frame;
forming one or more electrical connections between one or more terminals of the chip and one or more electrical lead portions of the corresponding lead frame;
encapsulating the lead frames by applying an encapsulant material over the lead frames and the street portions separating the lead frames;
back-patterning the bottom surface of the lead frames to remove the webbed portions and the street portions; and
singulating the encapsulant material disposed over the street portions to form individual chip scale packages.
2. The method according to claim 1 , wherein the chip attachment area is a chip pad area or a padless portion of the leadframe.
3. The method according to claim 1 , wherein the step of attaching the chip to the chip attachment area comprises placing the chip on top of active leads that support the chip in the absence of a chip pad, and affixing the chip using a non-conductive adhesive or a die attach film adhesive.
4. The method according to claim 1 , wherein the pull-in leads are arranged in a single row or in multiple rows around respective chip attachment areas of the lead frames.
5. The method according to claim 1 , further comprising electrical leads which are not in the form of pull-in leads.
6. The method according to claim 1 , wherein the back-patterning step is conducted using partial etching or flood etching.
7. The method according to claim 1 , wherein the encapsulation step is conducted by block molding or individual unit molding.
8. The method according to claim 1 , wherein the chip pad is solid or comprises one or more thermal vias.
9. The method according to claim 1 , further comprising affixing solder balls, solder finish, or solderable material to one or more electrical lands of the chip scale packages before or after singulation.
10. The method according to claim 1 , wherein the step of forming electrical connections is accomplished using vine-bonding techniques, flip-chip techniques, or a combination of both.
11. The method according to claim 1 , wherein the step of forming electrical connections is accomplished by connecting the terminals on the chip to the end portions of the electrical lead portions extending from the lead frame.
12. The method according to claim 1 , wherein lead portions, bottom of the block of lead frames, or both, are coated by a solder mask.
13. The method according to claim 1 , further comprising applying an electromagnetic interference shield to the chip scale packages before or after singulation.
14. The method according to claim 13 , wherein the electromagnetic interference shield is applied by electroless plating, electrolytic plating, spraying, dipping, sputtering deposition, or a screen printing process.
15. The method according to claim 1 , wherein the chips are attached to the chip attachment areas using a conductive epoxy, non-conductive epoxy, or die-attach film adhesive.
16. The method according to claim 1 , further comprising die-stacking one or more second chips on the tops of one or more chips before encapsulating the lead frames.