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Solder Ball Attachment: an equipment overviewAlignment 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
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 SpecificMachines such as Vanguard's are placement-dedicated, that is, they are specific to the placement process and do not include ovens for the reflow processĄ 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 SystemsLike 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 ChallengesWhenever 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.
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.
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.
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