US 2002/0000331 A1Published application

Method for making an electronic circuit assembly

OwnerVivek Amir Jairazbhoy, Thomas B. Krautheim +8inventors

InventorsVivek Amir Jairazbhoy, Thomas B. Krautheim, Mohan R. Paruchuri, Lakhi Nandlal Goenka, Jun Ming Hu, Jay DeAvis Baker, Edward McLeskey, Delin Li, Cuong Van Pham, Robert Edward Belke

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Abstract

A method for producing an electronic circuit assembly (e.g., a circuit board) from an etched tri-metal-layer structure which provides air bridge crossovers and specially designed bumps etched from a middle layer of the tri-metal-layer structure. The bumps are formed at particular circuit locations in order to provide interconnects for (1) heavy wirebonding, (2) fine wirebonding, or (3) direct chip attachment; or, to provide (4) lifters for assuring a minimum solder joint standoff height or (5) barriers for retarding solder joint crack propagation.

Claims27

Dependent claims

A method for making an electronic circuit assembly, comprising the steps of:

(a) providing a precircuit comprising:
(i) a metallic sheet made of a first metal and having a top surface and a bottom surface;
(ii) a first conductor pattern attached to the bottom surface of the metallic sheet and made of a second metal, wherein the first conductor pattern comprises:
(A) a base pad having a first predetermined size and shape and a base pad perimeter thereabout,
(B) a circuit trace, and
(C) first and second pedestal pads disposed proximate the circuit trace on opposite sides thereof;
(iii) a second conductor pattern attached to the top surface of the metallic sheet and made of a third metal, wherein the second conductor pattern comprises:
(A) a plurality of masking pads arranged generally within the base pad perimeter, wherein each masking pad has a second predetermined size and shape smaller than the base pad, and
(B) a bridging element having first and second enlarged ends and a constricted portion therebetween, the bridging element being oriented generally transverse to the circuit trace with each enlarged end disposed opposite a respective one of the pedestal pads;
and
(iv) a substrate having an electrically insulative surface to which the first conductor pattern is attached;
(b) etching the precircuit in an etchant which etches substantially only the first metal, so as to form undercuts in the metallic sheet directly beneath the masking pads;
and
(c) continuing to etch the precircuit and undercut the masking pads to create a circuit,
(i) such that the metallic sheet beneath each masking pad is substantially completely undercut causing the masking pads to detach from the metallic sheet, thereby providing a plurality of bumps made of the first metal disposed atop the base pad generally within the base pad perimeter,
(ii) wherein a pedestal made of the first metal is formed between each pedestal pad and its respective enlarged end of the bridging element, thereby providing an air bridge crossover above the circuit trace.

13 more elements

A method for making an electronic circuit assembly, comprising the steps of:

(a) providing a precircuit comprising:
(i) a metallic sheet made of a first metal and having a top surface and a bottom surface;
(ii) a first conductor pattern attached to the bottom surface of the metallic sheet and made of a second metal, wherein the first conductor pattern comprises:
(A) a plurality of base pads each having a first predetermined size and shape and a base pad perimeter thereabout,
(B) a circuit trace, and
(C) first and second pedestal pads disposed proximate the circuit trace on opposite sides thereof;
(iii) a second conductor pattern attached to the top surface of the metallic sheet and made of a third metal, wherein the second conductor pattern comprises:
(A) a masking pad generally centered opposite each base pad, each masking pad having a second predetermined size and shape generally congruent in size with the first predetermined size and shape of its respective base pad, and
(B) a bridging element having first and second enlarged ends and a constricted portion therebetween, the bridging element being oriented generally transverse to the circuit trace with each enlarged end disposed opposite a respective one of the pedestal pads;
and
(iv) a substrate having an electrically insulative surface to which the first conductor pattern is attached;
(b) etching the precircuit in an etchant which etches substantially only the first metal, so as to form undercuts in the metallic sheet directly beneath the masking pads;
and
(c) continuing to etch the precircuit and undercut the masking pads to create a circuit,
(i) such that the metallic sheet beneath each masking pad is substantially completely undercut causing the masking pads to detach from the metallic sheet, thereby providing a plurality of bumps made of the first metal, each bump being disposed atop a respective one of the base pads,
(ii) wherein a pedestal made of the first metal is formed between each pedestal pad and its respective enlarged end of the bridging element, thereby providing an air bridge crossover above the circuit trace.

13 more elements

A method for making an electronic circuit assembly, comprising the steps of:

(a) providing a precircuit comprising:
(i) a metallic sheet made of a first metal and having a top surface and a bottom surface;
(ii) a first conductor pattern attached to the bottom surface of the metallic sheet and made of a second metal, wherein the first conductor pattern comprises:
(A) a base pad having a first predetermined size and shape and a base pad perimeter thereabout,
(B) a circuit trace, and
(C) first and second pedestal pads disposed proximate the circuit trace on opposite sides thereof;
(iii) a second conductor pattern attached to the top surface of the metallic sheet and made of a third metal, wherein the second conductor pattern comprises:
a bridging element having first and second enlarged ends and a constricted portion therebetween, the bridging element being oriented generally transverse to the circuit trace with each enlarged end disposed opposite a respective one of the pedestal pads;
and
(iv) a substrate having an electrically insulative surface to which the first conductor pattern is attached;
(b) attaching at least one masking pad to the top surface of the metallic sheet generally within the base pad perimeter, wherein each masking pad has a second predetermined size and shape and is made of a masking material which may be stripped without significantly attacking the first, second, and third metals;
(c) etching the precircuit in an etchant which etches substantially only the first metal, so as to form a circuit having,
(i) a plurality of bumps made of the first metal, each bump being disposed beneath a respective one of the masking pads, and
(ii) a pedestal made of the first metal formed between each pedestal pad and its respective enlarged end of the bridging element, thus providing an air bridge crossover above the circuit trace;
and
(d) stripping the masking pads from the circuit, thereby exposing the bumps.

13 more elements

Dependencies are inferred from the claim text.

Facts

Application: 09/920,192Filed 1 Aug 2001
Priority: 4 Sep 1998
Published: 3 Jan 2002
Term ends: Not estimatedThe source records don’t support an estimate.

Classification26 codes

H05K 3/4685
Manufacturing multilayer circuits: manufacturing of cross-over conductors
H05K 1/111
Printed elements for providing electric connections to or between printed circuits: pads for surface mounting, e.g. lay-out
H05K 3/303
Assembling printed circuits with electric components, e.g. with resistors: with surface mounted components
H05K 3/4007
Forming printed elements for providing electric connections to or between printed circuits: surface contacts, e.g. bumps