September 1998
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Solder Ball Attachment: an equipment overview
Alignment accuracy and flexibility to handle different BGA package types and sizes are criteria that both users and manufacturers agree are essential for the solder ball placement process.By Ron Iscoff, Editor
Figure 1. This Shibuya system handles a range of BGA packages. |
As with any new technology, there are as many questions as there are answers, as users and manufacturers alike look for the ideal solution to the solder ball placement issue.
Several companies today offer machines for attaching (also often referred to as mounting or placing) solder balls to the BGA package where they act as the final interconnect to the PC board (Figures 1-3).
This placement is characterized by ball acquisition, ball-to-pad alignment and ball deposition (Figure 4), according to Scott D. McGill, director of business development and technology at RVSI Vanguard Automation Inc., Tucson, Ariz., who was instrumental in developing the company's BGA VAi 6300 ball placement system.
Placement Specific
Machines such as Vanguard's are placement-dedicated, that is, they are specific to the placement process and do not include ovens for the reflow process„ a component of ball attach. Ovens, however, are added inline.With few variations, all other equipment makers use a vacuum-pin approach to pick-and-place the solder balls onto the packages. That method, according to McGill, "greatly limits the substrate area and I/O that may be processed in a single cycle."
Vanguard employs a screen-printing gravity method that allows all balls to be placed on every pad in one cycle, regardless of the number of devices being processed or the I/O of the devices. McGill also claims that the Vanguard VAi 6300 system is the only one currently available that can be field upgraded from semi-automatic to fully automatic, high-volume processing.
Vision Systems
Like Vanguard, Shibuya, a Japanese maker of ball placement systems, does not manufacture a reflow furnace, and leaves the choice of oven up to the end-user.Shibuya currently offers several different ball-placement systems. The most popular, according to Harry Sorteberg, sales engineer for Marubeni International, U.S. distributor for Shibuya in San Jose, is the SBM 200. However, the SBM 300, with an onboard vision system, was designed specifically for CSPs, and one is now enroute to an undisclosed U.S. customer for that purpose, Sorteberg says. Shibuya has a modest presence in the U.S., but Hyundai Electronics, Korea, is probably its largest customer with machines in 16 lines.
Flux/paste deposition with the Shibuya machines is via a pin-transfer method, which uses a set of compliant/non-compliant pins that are dipped into a fine layer of flux paste. Pin-transfer will compensate for irregularities in the flux, according to Sorteberg.
Panasonic KME Create produces the BP10C-S and BP20C-S units for CSP ball placement. The BP 20C-S is for CSPs in strips and attaches solder balls between 0.3-1.0 mm in diameter. There are no units in the U.S., and Panasonic has not been actively marketing the units here, according to Shinji Harada, a sales engineer at Panasonic Create's San Jose office. Harada, however, says Panasonic has machines at some of Asia's largest packaging foundries.
Koses, a Buchon, Korea, company has entered the solder ball placement equipment market with the Model KAM-700. Eric Jeon, director of sales and marketing for the company, says Koses has machines installed at major semiconductor makers in Korea. The KAM-700 can process a minimum of four µBGA® strips/minute and includes full vision inspection.
Although it's likely that there will be several more new and unfamiliar names entering the ball placement market, companies like Motorola, which makes a wide range of assembly equipment, are now offering a ball placement unit.
Equipment Challenges
Whenever a new technology, such as ball placement, must be implemented, there are challenges, admits Vanguard's McGill. First, the lack of package and carrier standardization affects the equipment supplier's ability to develop a system that can provide high volume and high throughput within a single platform.
Figure 2. The Vanguard 6000 ball placement system handles strip or singulated parts. |
Finally, McGill adds, the emerging nature of BGA and CSP package development results in new package formats continually being developed. This can strain the ability of equipment suppliers to design new fixturing and processes to handle the growing variety of formats.
Other equipment companies are producing equipment which has not been designed specifically for ball placement. They contend, however, that their systems (which are typically centered around a furnace), will handle the ball-placement process from start to finish, solder reflow included. Examples are systems from Meco Equipment Engineers in the Netherlands and Scientific Sealing Technology in Downey, Calif.
Fluxless Systems
Figure 3. The Koses KAM-7000 offers vision inspection,
considered a mandatory feature from CSP use.
The Meco Interposer Bump System is a format-independent machine based on a tailored furnace with a very wide process window that can use low-flux or unfluxed processes.
The system automatically loads and unloads substrates, places the solder balls and reflows, with all operations integrated into one machine, according to Huge Menschaar of Meco.
While the system does not provide flux for ball retention, tests so far indicate that "flux is not required at all, in most cases," Menschaar adds. However, if the customer requires flux, Meco says tests indicate that a "no-clean"flux is sufficient. The Meco system measures 7 x 7.5 feet and is scheduled for beta delivery in December.
The Scientific Sealing Technology approach is also fluxless and, like the Meco process, is performed in a large, controlled-atmosphere furnace. The tooling for the furnace is composed of an upper and lower plate which are machined from graphite. Richard Ramos, SST's executive vice president, claims that the SST process saves considerable money over the additional capital equipment needed when a solder reflow oven is added inline to dedicated placement machines.
While several manufacturers of equipment for wafer bumping and solder deposition say their equipment can be used for ball placement, this is not always the case, explains Rick Godin, marketing director for MPM Speedline, Franklin, Mass. Godin says MMP's drop-on-demand, Metal Jet™ technology should not be confused with a method for ball placement; rather, it's designed to create bumps on silicon wafers, meant as an alternative to traditional flip-chip processing.
(For more about MPM's method, which is an adoption of MicroFab's Solder Jet™ technology, see the article by Drs. Hayes and Wallace in this issue.)
For users like Amkor Technology Inc., Chandler, Ariz., missing solder balls are the number one issue, according to Randy Rosier. "Equipment, tooling and solder ball material improvements are needed to ensure that apertures fill 100 percent of the time and that balls do not stick to the tooling due to ESD or foreign matter."
Next in importance, adds Rosier, is ball quality. The Amkor engineer would like to see improvements in ball diameter through better tolerance control, reduction of the tolerance range and the elimination of solder particles or foreign material. Rosier points out that under-sized balls may lead to an extra ball being placed in a site. Additionally, adhering solder particles can also lead to increases in reflowed-ball diameter.
Finally, Rosier says, complications associated with substrate warpage are a real concern. "This is a larger issue with film-based CSPs than with the more rigid PBGA substrates." Preventing flux transfer to the tooling is an associated warpage complication, he notes. Better flatness handling is also needed to reduce warpage, according to Rosier.
Robert J. (Jim) Walker, marketing director at the Integrated Packaging Assembly Corp. (IPAC), San Jose, is pushing for total consistency in solder-ball placement. "The solder-ball attach portion of the machine should dispense 100 percent of the balls consistently. The solder ball pickup head must also maintain a good vacuum, or it will not dispense 100 percent of the balls," he added.
Inline inspection is also a desirable system component, Walker says. In addition to checking for accuracy, the machine should verify ball coplanarity after placement and reflow. Currently, IPAC uses separate machines to check for placement accuracy and co-planarity.
Flexibility is another key factor, Walker says. "We want a machine that easily converts from handling strips to handling single units. That way we can assemble both cavity-up (molded) and cavity-down (encapsulated) BGAs on the same machine. Our existing system is not easily converted for use with single units in boats."
Figure 4. Standard ball attach process flow (courtesy RVSI Vanguard Automation)
Conclusion
As ball placement technology improves, users can look for machines that do more, occupy less space and offer greater flexibility. Today, fast throughput does not appear to have the same weight with most users as either ball placement accuracy or co-planarity. However, as the BGA market continues to grow, throughput demands will increase exponentially.
| Solder Ball Placement Equipment Contacts For more information on companies mentioned in this article, please contact: |
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| Company | Contact | Phone | Fax | |
| Koses (Korea) |
Eric Jeon | +82.32.662.2224 | +82.32.662.2214 | kosos@puchon.net |
| Meco Equipment Engineering (Germany) | Hugo Menschaar | +31.416.384.384 | +31.416.384.545 | |
| Motorola (Phoenix) |
Jim Carrigan | 602.437.1368 | 602.437.3848 | a14422@email.mot.com |
| Panasonic Create (San Jose) |
Shinji Harada | 408.895.1830 | 408.895.1831 | sharada@panasonicfa.com |
| RVSI Vanguard (Tucson) |
Jim Magoon | 520.297.2621 | 520.544.0535 | jmagoon@vai.net |
| Scientific Sealing Technology (Downey, Calif.) |
Richard Ramos | 562.803.3361 | 562.803.4043 | rramos@sst-tech.com |
| Shibuya Marubeni Int'l (Sunnyvale, Calif.) |
Sandy Truax | 408.727.8447 | 408.245.4525 | sandy@marubeni-intl.com |