Hitachi Metals, Ltd.

2005 News Release

September 28  

 

Manual Micro-ball Mounter Developed

—Capable of Mounting Two Million 80μm-Diameter Balls at a Pitch of 150μm on a 12-inch Wafer—

Tokyo, Japan, September 28, 2005—Hitachi Metals, Ltd. has announced today that it has announced the development of the world’s first, advanced manual micro-ball mounter capable of mounting two million 80µm- diameter, 150µm-pitch, lead-free solder balls1 at a time on 12-inch wafers2.

1. Background and Objectives

Demand for ever-higher performance in semiconductor devices is driving a search for higher signal transmission speeds and greater input/output pin density. To date, the mainstream in the transmission of electrical signals from semiconductor integrated circuits (chips) to printed circuit boards has been the wire bonding method (Figure 1) using highly conductive gold wires and lead frames. However, the use of solder balls in the ball grid array (BGA) method (Figure 2) is gradually gaining ground. The ball grid array allows not only rapid transmission at shorter transmission distances realized by the flip chip method³, but also higher density of circuits by reducing the diameter of the solder balls and consequently reducing the intervals (pitch) between balls. For this reason, there has been a growing need for solder ball mounters that can efficiently mount smaller diameter balls in higher density arrays on the surface of the wafers of which semiconductor integrated circuits are made.

Hitachi Metals last year developed a manual micro-ball mounter capable of mounting 500,000 100µm-diameter, 200µm-pitch, lead-free solder balls at a time on eight-inch wafers. Based upon this technology, Hitachi Metals continued in the pursuit of even higher performance, and successfully developed the world’s first manual micro-ball mounter (Figure 3) capable of mounting two million 80µm-diameter, 150µm-pitch, lead-free solder balls at a time on 12-inch wafers (Figure 5), and ball repair equipment (Figure 4) for reballing.

With this development, we have enabled the stable mounting of small diameter, narrow pitch lead-free solder balls onto 12-inch wafers, expected to become the predominant wafer size for semiconductor test production and R&D. This will make possible more highly advanced semiconductor design.

Hitachi Metals last year jointly developed an automatic micro-ball mounter. Based on that technology, and while moving forward with the development of a narrow-pitch manual micro-ball mounter, the Company will be engaged in the development of an automatic micro-ball mounter for smaller diameter balls at narrower pitches. We aimto set the world standard for such equipment.

Heightened environmental concerns and Europe’s RoHS Directive⁴ are speeding the adoption of lead-free solder balls. Hitachi Metals can offer a full range of total solution services in this field, ranging from high-precision lead-free solder balls to micro-ball mounters, and will continue its endeavors to contribute to he manufacture of higher performance semiconductor devices.

Figure 1. Wire bonding method	Figure 2. Ball grid array method

Figure 3. Micro-ball Mounter

Figure 4. Ball Repair Equipment

Figure 5. A mounted 12-inch wafer (Ball diameter 80µm/pitch 150µm /approximately 2 million balls)

2. Principles

(1)	A metal mask (a sheet of metal with holes in it) is placed on the wafer, and printing flux6 is pressed over it with the squeegee. The printing flux adheres to the surface of the wafer only where there are holes in the mask.
(2)	The metal mask is removed and a ball alignment plate with holes in the same places as the metal mask is placed on the wafer. The lead-free solder balls flow in, and a special squeegee brush7 is used to disperse the balls while at the same time pressing them into the areas where the holes in the mask were. And the ball alignment plate is removed. At that point, the balls are released from the ball alignment plate, and the viscosity of the flux causes them to adhere to the surface of the wafer. (The process to this point is performed by the solder ball mounter.)
(3)	Next, the wafer is placed in a solder reflow oven, where hot air fixes the solder balls in place.

3. Characteristics

(1)	Mounts 2 million balls per batch on a 12-inch wafer (maximum size, 300 × 300mm) Uses ball alignment plate (newly developed)8, special squeegee brush, and Flux (newly developed) Capable of mounting balls 80µm in diameter at a pitch of 150µm (previous equipment was limited to balls 100µm in diameter at a pitch of 200µm)
(2)	Limits the occurrence of extra balls9, and can be used even with substrates that have warped areas Uses a mask adhesion mechanism10 that prevents invasion of solder balls under mask.
(3)	Allows high-quality forming of bumps at low cost The uniform height of the bumps (coplanarity)11 is assured by the precision manufacture of the balls, making measurement unnecessary. In comparison to the plating method, there is more freedom to select the composition of the bumps12, in addition to which it has the strengths of holding changes in composition to a low level and allowing the use of lead-free solder. Because this is a dry process, wafer damage from corrosion or contamination is limited. Much less flux is used in flux printing than solder paste in paste printing, which means that the occurrence of voids within the bumps is greatly reduced. The cost for alignment plates is much lower than using the attachment mounting method13. Allows narrower pitch and a larger number of pins than paste printing14.

4. Micro-ball Mounter Specifications

	Existing equipment	Newly developed equipment	Existing equipment
System	Manual	Manual	Automatic
Dimensions	Printing unit 550W × 350H × 500Dmm Alignment unit 1,000W×450H×600Dmm	Printing unit 630W×270H×590Dmm Alignment unit 1,135W×580H×670Dmm	2,900W×1,600D×1,750Hmm
Wafer size	Maximum 200 × 200mm (8-inch wafer)	Maximum 300 × 300mm (12-inch wafer)	Maximum 300 × 300mm (12-inch wafer)
Ball diameter	Minimum 100µm	Minimum 80µm	Minimum 100µm
Mounting pitch	200µm	150µm	200µm
Mounting time	Less than 10 minutes, including time required for printing and mounting, excluding time required for mask alignment15	Less than 15 minutes, including time required for printing and mounting, excluding time required for mask alignment	Less than 5minutes for 8-inch wafers; less than 10 minutes for 12-inch wafers
Remarks	Released October 1 2004		Seller: Athlete FA Corporation

Specifications for the ball repair equipment are determined in response to customer requests.

5. Applications

(1)	Wafer and substrate development
(2)	Evaluation of the reliability of lead-free solder bumps (determining conditions for production of the optimal bump shape, including shape and dimensions of bumps after reflow, strength of connection to electrodes, bump composition and compatibility with electrode material)
(3)	Test production and semi-mass production of substrates and wafers

6. Suggested price

9.5 million per unit (masks sold separately, consumption tax included)

7. Number of patent applications

35

8. Availability

From October 2005

9. Sales target

5 units per year (Fiscal 2006)

10. Manufacturing and sales

Specialty Steel Company, Hitachi Metals, Ltd.

11. Other

This product will be on display October 4 (Tuesday) through October 9 (Saturday) at CEATEC JAPAN 2005, which will be held at the Makuhari Messe in Chiba Prefecture.

Customer inquiries:
		Syuhei Hayashi Specialty Steel Company, Hitachi Metals, Ltd. Telephone: +81-3-5765-4373 Facsimile: +81-3-5765-8317
Press inquiries:
		Akio Minami Corporate Communications Office, Hitachi Metals, Ltd. Telephone: +81-3-5765-4079 Facsimile: +81-3-5765-8312

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Additional information

Notes:

*1 Lead-free solder balls A terminal material used in new semiconductor packaging forms such as ball grid array (BGA) and chip scale packaging (CSP). Hitachi Metals led the world in developing the uniform droplet spray (UDS) method, a mass-production technology for forming solder balls. Using this method, solder balls are manufactured from a heated liquid-solder state directly into uniform-volume solder droplets, which are solidified in an inert gas environment. Compared with the conventional oil-based granulation method, this method raises the grade of reduced diameter balls, yielding balls virtually free of variations and enhanced surface properties, while also reducing manufacturing lead-time for greater productivity. Hitachi Metals is able to offer lead-free solder balls manufactured through this technology from as small as 80µm in diameter, providing high precision balls with untarnished surfaces and reduced diameter. As market needs heighten, we also plan to introduce balls of 50µm in diameter. *2 Wafer A chip or plate of silicon monocrystals, on which integrated circuits are formed. While eight-inch wafers currently predominate, production of 12-inch (300mm in diameter) wafers has also begun. *3 Flip Chip (FC) In connecting semiconductor chips to substrates, turning chips over enables the shortening of the distance between the chip and the substrate. This is an alternative to wire bonding. *4 RoHS Directive Regulations regarding the use of hazardous substances that will go into effect throughout the European Community on July 1, 2006. The use of six varieties of metals (lead, hexavalent chrome, mercury, cadmium, polybrominated-biphenyl, and polybrominated diphenyl ether) in electrical and electronic equipment will be restricted. *5 Bump A bump is an end terminal used in flip chip (FC) connection or in the connection between motherboard and semiconductor packages. Solder is used as a bump. *6 Flux A chemical substance used to activate surfaces to be fused during welding. Flux newly developed for this mounter keeps balls exceptionally well stabilized with minimal tainting of the printing mask. *7 Special squeegee brush A newly designed ball-transfer brush that prevents the occurrence of extra balls and enables the attaining of a high ball-transfer ratio with the minimum number of necessary balls. *8 Ball alignment plate This is a tool that determines the positioning of balls. Used together with the unique squeegee brush described above, balls can be rapidly aligned. *9 Extra ball This describes the condition when an excess solder ball has gotten into a solder bump opening that should contain only one ball. When this occurs, bump volume increases, causing unevenness in coplanarity and pulling on the bridge between bumps. *10 Mask adhesion mechanism This mechanism closely adheres the wafer/substrate surface to the mask to prevent balls from getting in between the wafer/substrate and the ball alignment mask. The adhesion principle is classified proprietary information. Conventional attachment mounting methods lacked in precision to compensate for warping of plastic substrates, limiting improvements to mounting ratios. Using this newly developed mask adhesion mechanism enables stable mounting even with warped substrates. *11 Uniformity of height (coplanarity) In FC connection or BGA/CSP bump connections, it is necessary that all solder bumps simultaneously contact corresponding electrode terminals. To improve connection reliability, solder bump heights must be as even as possible. *12 Selectivity of composition Compared with conventional tin-lead plating, regulating the eutectoid conditions of lead-free plating poses a significant challenge, and the composition fluctuates even in binary plating using tin and silver or tin and copper plating. On the other hand, using melted solder enables one to choose from all basic lead-free materials. For example, stable production of the currently predominant lead-free material Sn-3Ag-0.5Cu (Unit: % mass) poses a difficulty when the plating method is used. *13 Attachment mounting method As shown in the diagram below, this is a process through which balls are aspirated and released by a pickup arm, and then transferred to respective positions on the substrate where flux has been applied. Bulk mounting on large surfaces is technically challenging, with problems such as excess balls fixing onto the adhesive arm, or difficulties in transferring balls onto substrates with warps on the surface. *14 Paste printing Solder granules are coated to the surface of the wafer and substrate through lattice printing technology that uses a paste with mixed-in flux. At the mass-production level, this process is applied for bumps of 180µm in diameter and 300µm pitch. At the development level, mask openings with 70µm diameter and 150µm pitch are under testing, but currently still have problems such as the occurrence of voids within bumps and insufficient bump heights. *15 Mask alignment time The time required to align metal mask openings with electrode positions on the wafer/substrate.

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