Investigators: Frank W. Gayle, Carol A. Handwerker, Leonard C. Smith, and Maureen E. Williams

Technical Description:

The printing of solder patterns onto chips or circuit boards using ink jet printer technology is a novel means to avoid cumbersome screening techniques and environmentally unfriendly electroplating methods. In addition, "solder jet" technology is flexible (patterns can be input by keyboard) and capable of very fine pitch between solder deposits (< 100 µm). These capabilities are needed for the next generation of microelectronic packaging.

The NIST Metallurgy Division is working closely with ATP Awardee MicroFab Technologies, of Plano, Texas, and a consortium including Delco Electronics, AMP, Universal Instruments, Texas Instruments, Eastman Kodak, and Motorola, to bring ink jet technology closer to commercial reality. NIST scientists are focusing on materials compatibility issues involving the liquid solder and the jetting apparatus, and reactions between the jetted solder and the various substrate materials used in microelectronic interconnects.

Technical Objectives:

• Provide technical assistance to MicroFab in issues of materials compatibility.

• Collaborate with MicroFab and its customers in determining system requirements for reliable solder jet operation and for product (solder joint) performance.

• Characterize the behavior of solder jet deposits under a range of deposition conditions and substrates, including joints fabricated through reflow.

Anticipated Outcome:

• Materials compatibility issues of next generation devices for creating solder patterns will be developed.

• Solder joint formation after reflow for solder deposited using jet technology will be better understood.

Accomplishments for FY 1995:

• Interfacial reactions associated with containment of Pb/Sn solders in stainless steel reservoirs have been identified and possible solutions to the concomitant contamination have been investigated.

• Problems associated with oxidizing atmospheres during jetting have been identified. Improvements in jetting and in deposit morphology using controlled atmospheres were characterized.

• Identification of processing windows for substrate temperature, jet height, etc., which allow necessary wetting of substrates but without excessive interfacial reaction. Certain conditions unfavorable to reflow were also found.

• Evaluation of physical and mechanical property data for In-Sn alloys which are necessary for ultrasonic jetting devices. These data were supplied to MicroFab in the form of a computer program which provides data for any composition and temperature.

Impacts and Technical Highlights:

• Our identification of solder oxidation problems contributed to MicroFab's decision to add nitrogen co-flow to the solder jet apparatus. This control of oxygen is necessary for MicroFab's milestones both for operation of the solder jet and for formation of reliable solder joints.

• Wettability problems which we have identified with respect to copper substrates have led to investigations of means (such as imidazole coatings) to enhance wettability. This is essential for MicroFab's milestone to form reliable solder joints with solder jet technology.

• Research at the Metallurgy Division has identified temperature regimes which are suitable for deposition onto Au-coated silicon. This is essential for MicroFab's milestone to form reliable solder joints with solder jet technology.

• The amount and valence of oxide formed on copper coupons aged under different conditions can be determined by galvanostatic reduction. Reproducibility within a given set of coupons is quite good. Cu₂O was the primary species detected for all levels of aging; however, two of the aging conditions resulted in 1-2 monolayers of CuO on the outer surface.

• Electrochemical reduction is an excellent technique for determining the oxidation state of copper, both qualitatively and quantitatively. These measurements can be performed directly on printed wiring boards and component leads and may eventually be used to assess solderability.

Back to Table of Contents

Last modified: Mon Jan 06 09:46:15 1997 Metallurgy Webmeister