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SELECTIVE IR SOLDERING PROCESS

IP.com Disclosure Number: IPCOM000004677D
Original Publication Date: 2001-Apr-02
Included in the Prior Art Database: 2001-Apr-02
Document File: 2 page(s) / 7K

Publishing Venue

Motorola

Related People

Timothy B. Dean: AUTHOR [+3]

Abstract

Some components are not easily soldered using typical reflow or waveline processes; these parts are not amenable to batch processing. A program required a method to solder seal a lid on an on-board hermetic enclosure that was incorporated on a substrate meant for a non-hermetic application. The hermetic enclosure was a rectangular solder-coated ring soldered to a substrate. Solder sealing the lid to the enclosure had to be accomplished without subjecting the accompanying components on the substrate to excessive heat. Our solution was to use a stencil or mask with apertures that allowed only the solder on the lids and seal rings to be melted by an IR lamp, thus protecting the surrounding circuitry from excessive heat. This approach selectively soldered only the components that needed to be soldered, and it protected the surrounding circuitry from excessive heat. This paper discusses the use of the selective IR soldering process for an on-board hermetic package.

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SELECTIVE IR SOLDERING PROCESS

by Timothy B. Dean, Charles R. Delott and Scott D. Serlin

Abstract Some components are not easily soldered using typical reflow or waveline processes; these parts are not amenable to batch processing. A program required a method to solder seal a lid on an on-board hermetic enclosure that was incorporated on a substrate meant for a non-hermetic application. The hermetic enclosure was a rectangular solder-coated ring soldered to a substrate. Solder sealing the lid to the enclosure had to be accomplished without subjecting the accompanying components on the substrate to excessive heat. Our solution was to use a stencil or mask with apertures that allowed only the solder on the lids and seal rings to be melted by an IR lamp, thus protecting the surrounding circuitry from excessive heat. This approach selectively soldered only the components that needed to be soldered, and it protected the surrounding circuitry from excessive heat. This paper discusses the use of the selective IR soldering process for an on-board hermetic package.

SELECTIVE IR SOLDERING PROCESS

A program was in need of a means of housing a monolithic filter crystal originally contained in an HC-45 style package.

The method of housing had to reduce the overall form factor so that the part could be incorporated in a stacked substrate assembly with limited headroom.

Making an on-board hermetic enclosure on a portion of a substrate to house the filter crystal seemed to have merit.

The components associated with the crystal circuitry would populate the rest of substrate. The enclosure consisted of sliced rectangular Kovar tube stock plated with eutectic solder.

The lid was chemically machined Kovar sheet stock plated with eutectic solder. An infrared heat source was used to solder seal the lid to the enclosure.

The rectangular ring was clamped to the substrate along with a rectangular ring that supported the perimeter of the substrate.

The assembly was fluxed and put through a reflow oven,

To obtain the optimal size reduction, the size of the filter crystal had to be decreased. After testing different sizes for electrical performance, the optimal size was found to be .090" x .110".

The filter crystals were mounted in the enclosure and tested electrically.

The lids were equipped with flaps on the sides designed to grip the sides of the enclosure to hold the lid in place prior to the solder sealing process.

The substrate assemblies were placed in a fixture with apertures coinciding with the lidded enclosures.

The fixture containing the substrate assemblies with crystal enclosures was placed atop a fused quartz window. A highly reflective parabolic enclosure with a 1000 watt IR lamp was affixed below the window. The IR lamp was ramped up to 20% power for five seconds to preheat the parts and the lamp filament. Then the lamp was ramped up to the power necessary to seal the enclosure, which in this case was 85%, for ten seconds.

While the apertures in the fixture allowed the IR e...