Augmented Hydrostatic Extrusion of Ultrafine Gold Wire

Topics:

1. Foreword
2. Status Report
3. Accomplishments
4. Marketing

1. Foreword

When making ultra-fine wire, as the wire gets finer, processing becomes more difficult. The possible reduction per die decreases, the possible drawing speed drops and the wire breaks more often. Furthermore, the smaller the wire the harder it becomes to maintain uniform wire diameter. The diameter fluctuates excessively. However, with our "Augmented Hydrostatic Extrusion" (HYDRAW) equipment we are able to extend beyond some limitations of the present day conventional processes. Reductions up to 25% per die (even for hyper-fine gold (Au) wire) are possible, wire breaks rarely occur, and the wire size remains uniform. Presently we make wire of uniform diameter down to 0.4mil. There is no demand in the foreseeable future for wire size smaller than 0.4mil.

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2. Status Report

State of the Art

Tanaka of Japan, is the world's major supplier of gold bonding wire. Tanaka already makes 0.8mil (20µ) gold bonding wire commercially. They also make 0.7mil (17.5µ) stud bump wire commercially. Today's automated ultrasonic bonding machines are capable of bonding wire down to those sizes. Currently only chips for special applications require wire below the 0.7mil size. Chips for such applications are bonded by manually operated wire bonding machines. This wire size slows down the rate of production. These are special applications for military and aerospace products only.

Flip (back to back) chips, bonded by ball bumps, are becoming more and more popular. Wire contacts are replaced by tiny balls (bumps) that are bonded to the chip. The chip is then flipped onto leads, and bonded, back to back, in one step. The bumps are produced from ultra-fine wire. Flip chips are becoming more dense, and the current bumps are made from 1mil wire with some applications using 0.7mil. The vision of the major chip makers (and users) is to make the bumps from smaller wire, down to 0.4-0.5mil.

The bulk of the current ball bumps are made from 1mil wire. This wire size dictates a pitch of at least 100µ. In the race to make smaller chips with a larger number of leads, some makers have started to use bumps from 0.7mil wire. The pads are closer, with a pitch of 70µ, allowing a larger lead count ("denser chips").

Presently the factor limiting the density of the chip is the size of the wire that can be produced reliably, economically, and with uniform diameter. Because the pad size has to be 2 to 3 times larger than the wire from which the ball bump is made, a 0.7mil wire dictates 40µ pad size which in turn mandates a pitch of 50 to 60µ. Wire size of 0.4mil is as small as present day technology may demand.

Research and development now focuses on the next step, where the pads will be replaced by other means of bonding and the need for wire will be eliminated. Such developments are looming over the horizon, but are not yet a reality. Furthermore, the potential uses of ultra-fine wire stretch beyond the bonding wire market.

All the wire makers now feel the pressure to make finer size gold bond wire, for wire bonding for standard chips and for stud bump bonding for flip chips. Typical major limitations for wire smaller than 2mil are:

1. The possible percent reduction in area per die is less than 4%.
2. The speed is less than 1000 feet per minute.
3. Uniformity of the wire becomes poorer and poorer. The diameter fluctuates by about ±5% for a 1mil wire and even more for smaller wire.
4. Wire breaks more often into smaller lengths.

We at Metalforming Inc. can make 0.4mil gold wire on our Hydraw machine. This wire can be used by chip makers, as a conventional bond wire, as well as stud ball bump wire for the flip chip.

We have used wire from three of the five major suppliers of gold bond wire and found that their wire was not uniform in diameter, fluctuating by as much as ±5%. Even when we fed their (1.5 or 2mil) wire into our Hydraw machine as raw material we were able to reduce it down to 0.4mil and restore the uniformity of the diameter.

Comparing our capabilities with the state of the art we find:

1. Our 1mil wire is the most uniform wire available. The 1mil wire by other wire makers was irregular in size. We can make a much more uniform wire.
2. Only Metalforming Inc. can make wire below 0.7mil reliably and economically.
3. In addition, our process offers an alternative, to wire makers, that have problems maintaining uniformity at any wire size.

These comparisons are tabulated below:

Criteria	WET DRAWING	HYDRAW
% Reduction in Area per Die	4% or less	25%
Speed	?	800 ft/min
Wire Breaks	frequent	seldom or none
Diameter Fluctuations	+/- 5%	< 0.2%
Minimum Wire Size	0.7mil	0.4mil

 

Window of Opportunity

Foreword

The most attractive and achievable goal for Metalforming Inc. is to enter into a partnership with a major established fine wire manufacturer or chip maker. This manufacturer/chip maker could supply us with the raw wire of about 2mil and Metalforming Inc. will reduce it to the desired size. Thus, we will only do what the Hydraw process is good for, i.e., reduce the wire in the range from 2mil down to 0.4mil. The exact transition point may shift up or down from 2mil, depending on the quality and economics of the source wire. Both wire makers and chip makers are interested in having more than one supplier of the small size wire.

Even if we perfect our process further, we still face the necessity to enter into the relationship described. The major thrust of our promotional effort should shift into developing a strategic partner relation. Preferably, but not exclusively, such a partner may be a wire or chip maker.

Wire Makers

All gold bonding wire makers have smelting facilities and technology. They also have standard wire producing equipment and personnel. We can avert the need to develop smelting capabilities at this time. We can enter the market as a sub-contractor to an established wire maker, or to the end-user, the chip maker.

Most wire makers cannot produce wire below the size of 1mil. We can produce such wire economically on their behalf. They will supply the source wire and we would reduce it to 0.7 and even to 0.4mil wire when requested. These makers are under pressure to come up with products that compete with Tanaka's 0.7mil wire, and we can offer them a solution. They are under pressure because they don't want to disappoint their customers requiring larger diameter wire, and lose the 0.7mil niche to Tanaka. Their customers cannot tolerate, indefinitely, a single source supply situation.

Chip Makers

We may offer the chip makers access to the much desired 0.4mil wire, which they cannot get anywhere else. They will provide us with a 1 or 2mil wire (which they get from their regular source) and we will reduce it for them to 0.4mil. Chip makers have all the remaining technologies needed to produce chips with 50µ pitch. They wish to produce that chip, if they could only have a reliable source for an inexpensive 0.4mil wire.

These are our niches, or windows of opportunity, to penetrate the market.

The time is now ripe for this step. We learned that some wire makers are pressured by major customers to supply them with 0.7mil wire for their flip chip. They must do it to satisfy a good customer, but due to production or economical considerations prefer not to assume this responsibility. We were asked to supply chip makers with test quantities to verify our reliability.

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3. Accomplishments

• A fully functional Mark1 HYDRAW Unit for the manufacture of wire samples was constructed. Presently it is manually operated and controlled.
• Expertise in the process and operating of the equipment, especially on the setup procedures, was dramatically improved.
• Gold wire of down to 0.4mil diameter was repeatedly drawn with a 20-25% reduction in area through a single die.
• Speeds of 800 feet per minute (down to 0.7mil) and 250 feet per minute for smaller sizes are routinely running with uniform wire diameter and without wire breaks.
• The proper blend of regular and "vanishing" oils was determined, for optimal Hydraw performance and easy removal from the surface of the wire.

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4. Marketing

Potential Market:

By Size:
Standard bond wire down to	1.0mil
Present smallest bonding & bump wire diameter	0.7mil
Expected next generation stud bump wire diameter	0.5mil
By Length:
World consumption by year 2000 for all sizes in km/month
Bond wire	500,000
Bump wire	90

Potential Strategic Partnership:

Metalforming Incorporated is an enterprising company with a deep rooted base in many traditional metalforming processes and the progressive development of new technologies. In addition to its sound scientific background and accreditation, it is an entrepreneurial company ready to consider mutually beneficial relationship with established companies. The form of these relationships can be from consulting, training and process optimization to new technology licensing and limited partnerships.

The Hydraw project by Metalforming Inc. is now ripe for implementation as a manufacturing reality. We are open to offers of strategic partnership.

The project was presented at:

Technology 2007
"Technology Transfer - Today for Tomorrow"
September 22-24,1997
Hynes Convention Center, Boston, MA

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