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Method for solder-column preform extrusion for second-level interconnections

IP.com Disclosure Number: IPCOM000018909D
Publication Date: 2003-Aug-20
Document File: 3 page(s) / 88K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method for solder-column preform extrusion for second-level interconnections. Benefits include improved reliability, improved process simplification, improved yield, an improved development environment, and improved cost effectiveness.

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Method for solder-column preform extrusion for second-level interconnections

Disclosed is a method for solder-column preform extrusion for second-level interconnections. Benefits include improved reliability, improved process simplification, improved yield, an improved development environment, and improved cost effectiveness.

Background

The conventional solution for solder-ball placement and flux application results in several problems, including:

•         Capital equipment expense

•         Yield loss associated with ball placement issues and ball-to-flux/paste alignment

•         Second-level BGA interconnection expense

•         Long collateral ordering and preparation time for items such as stencils, ball pick-and-place (PnP) head, vision masks, and solder materials

•         Development costs

•         High substrate warpage at the ball-attach process

Conventionally, processing equipment applies flux to land-grid array (LGA) substrate lands by paste printing and uses carrier fiducials for alignment. Ball placement equipment uses a pick and place ball head to place solder spheres on ball-grid array (BGA) substrate lands and uses carrier fiducials for alignment. Fluxing materials and solder spheres are applied independently to the package body. Alignment of the sphere and package to each other and to the land is required. If an item is misaligned or is incomplete, touch-up is required or the device is unusable (yield loss).

         Conventional fluxes are heat activated. They can vary from a thick paste to a liquid, depending on the solvent concentrations. Solder preforms used in the electronics industry have external flux coatings. Tacky fluxes are offered commercially for PCB assembly, including BGA interconnections. Fluxing technologies use a concentration of resin solids with a solvent carrier, such as isopropyl alcohol. Fluxes are available with various solids concentration ranging from 25% to 40%. Standard protocol for use of fluxing agents includes the maintenance of viscosity to control the application by using solvent thinners.

Conventional pick and place ball heads are product specific and expensive. A long lead time exists for obtaining pick-and-place ball heads, ranging from 4-8 weeks.

High substrate warpage can cause cracking and poor solder joints.

General description

The disclosed method is an extruded solder column embedded in a preform phase-change flux material. The preformed sheet contains the interconnect pattern for a BGA device, controlling the pitch and position of the solder columns. The phase-change material contains the fluxing agent required to...