An Independent Journal Dedicated to the Advancement of Chip - Scale Electronics January - February 2000 Email the editor

Speed, repeatability and placement accuracy continue to be the buywords for solder ball placement. Flexibility, with fast changeovers for different substrate size has also become a mandatory.

By Ron Iscoff, Editor

Given the cost of capital equipment, coupled with the industry's recent downturn, it's not surprising that improvements to solder ball placement systems since our September 1998 survey have been modest and not revolutionary. Ball placement systems are employed to attach solder balls to area-array package substrates where they form the final interconnection to the substrate. They may, depending on the equipment, also be used to bump the complete wafer for wafer-level processing. Figure 1. The RVSI Vanguard Vai 6300 system.

For now, the equipment represents largely a homegrown market, led by Motorola Manufacturing Systems, RVSI Vanguard (figures 1 and 2) and Scientific Sealing Technology (figures 3 and 4). One of the newer entrants to the market is KOSES (figure 5), a Korean company.

The Europeans are represented by Meco Equipment Engineers (figure 6), a Dutch firm, and the Japanese suppliers importing to the U.S. are Misuzu and Shibuya. Although Panasonic manufactures solder ball placement equipment, the company has declined to enter the U.S. market, for now, citing what it considers a too-small customer base.

A key decision between equipment is whether users prefer a stand-alone system that handles the complete ball attach process, or an in-line, modular system, where ball attach is one part of the attachment process.

The trends today, according to Dr. Gerald K. "Skip" Fehr, vice president of operations/CTO at IPAC, San Jose, are the move to "smaller balls and more of them. The CSPs in strip form are now requiring the 0.4 and 0.3 mm balls in very large quantities per strip."

This requires, adds Dr. Fehr, more placement accuracy, and better handling since the balls are small and light. "The problems will become greater with a changeover to lead-free solders," he notes, since the balls will be even lighter than they are now. Figure 2. An integrated Vai 6300 ball attach line.

There is no question, he says, that ball attach will be affected by lead-free requirements. "I'm not sure exactly what it will mean, but at a minimum, the temperature profile will change, which is likely to require changes in design and substrate materials."

Key issues in ball mounting, according to Anthony Sun, director of packaging technology at Siliconware USA, the U.S. office of Taiwan's Siliconware Precision Industries, include ease of device change, machine throughput and ball inspection.

"The system should be capable of changing from one ball count to another in a very short time," Sun says. "In addition, the ball placement tooling kit should be flexible when used with the same size package, regardless of the ball population."

Sun contends that a major equipment bottleneck occurs within the ball mounting process, either due to vacuum error, ball pickup retrys or simply because the index time is too slow. Vision inspection is needed, Sun adds, after the ball is mounted to ensure that all balls are on the package and aligned. Figure 3. A Scientific Sealing Technology unit.

Another choice users have to make is selecting either a system that uses flux, or one that doesn't. Meco and Scientific Sealing Technology are flux-free, the others are not.

As area-array packaging continues to bite into markets formerly held by traditional lead-based packages, users can look for ball placement equipment to get smarter, unflinchingly accurate and repeatable in its placements. Figure 4. Process equipment diagram for SST equipment.

Figure 5. KOSES KAM 710 system can be used in-line or as a stand-alone unit.

Figure 6. The Meco Engineers' MIBS includes a reflow oven.

How Do They Work?

We asked several of the makers of solder ball placement systems how their equipment works and what makes it unique. The answers, edited for space and style, appear below:

KOSES

System Description

The KOSES solder ball attachment systems are fully automatic from the autoload magazine loader to offloading to any reflow system. The KAM 710 is configured for BGA/CSP production, and features an automatic loader with flux transferred by a unique pin-type transfer. Ball attach includes an ejector, vision inspection and offloading to reflow.

The KAM 750 can handle BGA to wafer-level packages inline. The KAM 800 (wafer-level system) is similar to the KAM 710 and KAM 750, except that it features a separate pattern-controlled flux transfer and ball attach tool, plus mapping control software. Machine dimensions are (W) 18 meters x (D) 1.5 meters x (H) 17.5 meters

Special/Unique Features

• Special plating requires no periodic cleaning
• Separate pin control to eliminate package warping
• Easy tool changeover (less than 10 minutes)
• Designed for small ball sizes and fine pitch

Meco Equipment Engineers B.V.

System Description

The Meco Interposer Bump System (MIBS) is a fully automatic ball-placement system with an integrated reflow oven for bumping BGAs and CSPs. The product strips are placed with mold cap up on a format plate, and this "sandwich" is placed in a carrier. The format plate holds the pattern of the balls and the carrier becomes part of a chain of carriers.

The chain enters the process part of the system and builds a free-hanging loop in which the solder spheres can roll inside and fill the holes in the format plates. The filled plates, underneath the substrates, enter the reflow part of the system. In preheat, reflow and cooling zones, the spheres attach to the gold bumps on the substrates. After leaving the system, the product strips and format plates are separated invidually and continuously. The format plates enter the next cycle and the product strips are checked by the vision system and placed into a magazine.

Special/Unique Features

• Fully integrated, continuous ball-placement and reflow system, fully enclosed within a controlled and monitored atmosphere
• Operates with a minimum of no-clean, low-residue flux
• Equipped with universal carriers to handle both strip and singulated units
• Fully automatic, operator-independent load and unload robotics

RVSI Vanguard

System Description

The fully configured Vanguard Vai 6300 performs material handling, fluxing, ball placement and vision inspection functions. It is based on a modular platform that allows increases in throughput and automation with the addition of field-installable upgrades to the basic system.

Material handling is accomplished with an auto-width adjustment handling system for easy material load, unload and device changeover. Flux deposition is accomplished through a screen printing process, which can accommodate all flux types and volume requirements.

Solder ball placement is enabled by Vanguard's patented solder ball placement mechanism for extremely fast and repeatable ball placement of all balls on all pads of the substrates in a single cycle. The system features a post-placement 2D vision system for highly accurate and fast verification for 100% ball inspection.

The Vai 6300 integrates easily into a ball attach line, which includes reflow, clean and material handling processes.

Special/Unique Features

• Processes PBGA, CBGA, CSP and connector packages in single devices in boats, trays or strip formats in magazines on a single platform
• The ball-placement process allows simultaneous placement of all balls in a single cycle, and is capable of processing in excess of 15,000 balls in a single cycle
• The system is designed to allow the end user to group together two or more systems to decrease cycle time and increase throughput
• Small footprint, 1.3 m x 1.1 m

Scientific Sealing Technology

System Description

Scientific Sealing Technology systems incorporate the use of graphite as the resistive heater with an environmentally controlled atmosphere. This resistive heater fixture not only acts as a heating element, but also acts as a piece-part holder.

Typical profiles always include a vacuum step, which aides in removing the contaminates within the system, then the chamber is replenished with a clean process gas, as required, for the reflow step. The systems can heat as slowly as 0.5^oC/sec. to upwards of 5-6^oC/sec.

SST systems feature three major components: a process chamber, a microprocessor controller and a power pack/transformer.

The process chamber enables an airtight seal to be held while providing an environment for reflow. The controller compares the programmed heating rate to that of an embedded thermocouple in the tooling and makes the necessary adjustments, so that repeatable and reliable process parameters can be achieved. The power pack allows the required current to be supplied so that the graphite tooling can be heated at a consistent rate. This controlled environment enables void free and flux free attaches from pre-programmed profiles.

Special/Unique Features

• Complete "package" uses far fewer utilities than the average reflow furnace
• By eliminating flux, cleaning steps and voids are also eliminated
• Tooling employs no adhesives to hold devices
• Sealed environment allows hermetic sealing to take place