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By Terrence Thompson, Senior Editor [chipscalereview.com]
| | The makers of dispensing, encapsulating and underfilling tools have been involved in an evolutionary process for decades. Their equipment keeps getting better, faster, more precise (but not necessarily cheaper!) and frequently more software-driven. At the end of the day, the question is, just how much machine do you need? Read on to learn the finer points of equipment selection. | |
 | | “Technology is like fruit,” says Asymtek’s Steve Adamson. “You have to pick it at the right time!” |
If your applications involve dispensing, encapsulating or underfilling, just how much system do you need?
Whatever you’re looking for, you will probably find it at one of several vendors, if the price is right. (See the vendor listing that follows this article.)
The only thing worse than not getting the features you need, however, is paying for features you don’t need!
The basic equipment used to dispense underfills and encapsulants continues to be refined; innovative processes are gaining footholds. Yet dispensing/encapsulating machine performance remains inextricably intertwined with material sets.
“The industry is always evolving, and we saw several new underfill approaches developed in 2005,” notes Steven Adamson of Asymtek Inc., Carlsbad, Calif.
“I often say ‘technology is like fruit, you have to pick it at the right time!’ If you are too early, no one wants it; too late and it’s no longer needed.”
 | | The benchtop Allteq L1520e dispensing system |
We’re Talking Protection Folks!
The primary reasons to underfill and encapsulate are to protect ICs from—at a bare minimum—expected temperature excursions and less-than-perfect chip and substrate planarity that occur during manufacturing.
Underfills also minimize end-user negligence and environmental “dirt.” As more products become lighter, more portable and wireless, expect more unintended, but severe abuse.
Higher Integration Changes the Rules
Asymtek’s Adamson says, “We are seeing many systems that dramatically reduce the number of components by using higher levels of silicon integration.
“Many cell phones now use one or just a few chips. In the past, there would have been more die and discretes. We see designs converting to array-area packaging with much less business in traditional wire-bonded packages. Hence, there is much less business in dam-and-fill encapsulation.”
 | | The ASM DS500 features a 400 x 400mm dispense area. |
Adamson also notes that, “Product designers use techniques that minimize transient shocks. For high-end mobile phones with PDA features, manufacturers want underfills for higher reliability.
“Last year was a very robust one for encapsulation underfill equipment sales,” Adamson reports. Additionally, he notes, “the demand for reliable, portable equipment is driving manufacturers to expand the use of underfills.”
New Levels of Accuracy
Two sustained industry trends—the miniaturization and increasing densities of components—are forcing electronics makers to reassess their packaging and production processes, observes Hugh Read, product manager for Speedline’s Camalot Dispensing Products in Franklin, Mass.
“In the dispensing process, a platform that delivers high yield and high throughput is no longer enough,” Read maintains. “To meet OEM demands and stay competitive, today’s dispensing systems must also attain never-before-achieved levels of accuracy.”
The positional accuracy of the dispense mechanism in a platform’s specs should represent the real-world error of the system, he notes. “In short, the actual platform capability must be better than this specified value.”
 | | Asymtek’s Spectrum S-820 series jetting dispensing system |
Read says users should “fully evaluate the capability of their equipment versus the physical limitations or restrictions of other technologies; speed and accuracy specs must reflect the true conditions rather than an offering of best-case scenarios.”
Is There a Technology Gap?
Dr. George Riley of FlipChips Dot Com in Worcester, Mass., notes “The trend is to smaller packages. No surprise here.
“The question,” adds Dr. Riley, “is going to be how to make smaller dots of materials and fill tighter gaps under devices because increased silicon integration means ICs will get larger. Jet dispensing is able to address some of these questions. However there is a technology gap today.”
Materials guru Dr. Ken Gilleo of ET Trends LLC in Warwick, R.I., says, “First, there seem to be two opposing trends in packaging: higher performance with a slight-to-modest cost premium and the ever-popular cheaper that works most of the time.”
Since material costs have risen sharply due to Europe’s RoHS (Restriction of Hazardous Substances) legislation, copper, encapsulants and lead-free solders, design and processing are being pushed—or squeezed.
“Many preach that equipment cost is secondary to throughput,” says Dr. Gilleo, “since there are fewer cost pressures on packaging equipment that provides higher throughput and increased yield.
 | | The Datacon 2200 apm series system at work |
Machines at Half the Price?
“For instance, one equipment vendor claimed that Mainland Chinese users initially wanted machines that lasted half as long at half the price. Yet, once they understood that cost has less to do with durability and everything to do with precision, speed, and defect reduction, there was less resistance to more capable, higher-priced machines,” notes Dr. Gilleo.
Solder Joints
Lee Smith of Amkor Technology in Chandler, Ariz., says, “Historically, our focus in underfills has been for Flip-Chip-in-Package (versus BGA to mother board) and improved board-level reliability of CSPs to avoid underfill.
 | | GPD Global MiniMax |
“We have done extensive work in material-set optimization for lead-free applications.
“We are also exploring some other trends,” adds Smith. “The transition to underfill jetting instead of capillary flow to improve throughput seems compelling. Also, we need more emphasis on repair-able underfills to salvage PWB assembly if component(s) must be removed.
“With higher value portable multimedia products,” adds Smith, “the need to protect solder joints from mechanical shock stresses is more crucial.
“We see several trends driving increased demand for BGA underfills. First, there is the increasing die size for wafer-level- packaging (WLP) applications. Also, the transition from 0.5mm to 0.4mm pitches in CSPs and WLP allow either more I/O per package or die size- or package-size reductions.
| | The primary reasons to underfill and encapsulate are to protect ICs from— at a bare minimum—expected temperature excursions and less-than-perfect chip and substrate planarity that occur during manufacturing. | |
Flow Faster, Cure Faster
“Underfill materials must flow faster, fill tighter gaps and cure faster,” says Smith. “This may require the removal of fillers which can cause problems with reliability and performance.
“Underfills must be compatible with a broader range of lead-free solder pastes and flux materials. We have seen, and are hearing about many underfills that have their cure profiles inhibited or even prevented by certain solder pastes or flux materials,” cautions Smith.
Underfills with better Tg and CTE properties should be tailored for processing, cost and performance. Currently, there are underfills designed for throughput and flow performance that significantly degrade in the temperature cycle life of lead-free solder ball joints.
What it amounts to, Smith maintains, is the disintegration of the electronics supply chain. “This requires suppliers to improve communications on these issues so that standard process and material sets can be characterized across a wider range of applications to reduce obstacles for adoption.”
 | | The Hesse & Knipps DJ335 |
World-Class Machines
Another often overlooked factor, adds consultant Gilleo, is that the best machines run great software. “I think that machine software is where U.S. and European machine builders are winning. This very complex software is patented, often machine-specific, and not easily misappropriated. A would-be cloner is not knowledgeable enough to hijack the software.
“Yes, they can copy it, but even small differences in dispensing equipment mean it won’t run. So whom do you call for help, the company you pirated it from?
“Both Microsoft and IBM have been successful with this approach.”
“Low-labor-cost countries may buy simpler machines since they want to keep inexpensive higher labor content,” adds Dr. Gilleo.
“China does not really want ‘lights out’ factories. But the U.S., Europe, Japan and many Asian countries want maximum automation. Their ratios of engineers to semi-skilled labor is higher, so they want to keep their engineers busy.”
 | | The Speedline Technologies Camelot XyflexPro DLM dispensing system |
Minimalist Packages
Dr. Gilleo acknowledges that low-cost package design is becoming minimalist.” Area-array packaging is one good example.
The ceramic leadless chip carrier was developed decades ago as the best solution for hermeticity. Later, notes Dr. Gilleo, IBM added solder balls and columns (CBGA, CGA). Motorola and others changed the substrate to organic and the PBGA was born as Ompack.
Today, many assemblers remove the solder balls and call it a QFN, a format that’s available in ceramic, thermoset and thermoplastic. Look closely at the ceramic QFN and you will see the old LCC. So what’s old is new again. Removing this solder does away with the lead content, and selecting a lead-free solder is easier. The plastic QFN may be the lowest-cost package today.
Newest Challenges
Joe Fjelstad of SiliconPipe Inc. in San Jose, Calif., observes, “While encapsulants have often been seen as one of the more prosaic elements of the electronic packaging process, encapsulants serve a vital and increasingly important role in IC assembly, especially as greater numbers of IC packages are in stacked format and at chip sizes where the role of the encapsulant is magnified.
“There is a general tendency for electronic design and assembly engineers to think of IC packaging encapsulation only in terms of its ability to protect the IC physically from damage during assembly and use.
“However,” adds Fjelstad, there are many very important roles that encapsulants must play if the IC is to function reliably over long periods of time.”
Lead Free, Less Reliable
“With the European Union’s well-meaning, but sorely misguided imposition of lead-free solder looming darkly over the electronics industry, the significance of the encapsulant is increased.
“Prospective solutions have been forthcoming from resin formulators but there has been a simultaneous reduction in expectations for long-term reliability and package moisture sensitivity,” cautions Fjelstad.
Dispensing technologies have made significant improvements over time with newer, faster methods being introduced.
One long-standing concern relative to the encapsulation process is wire sweep and wire shorts.
TI’s bottom gate injection molding process, introduced many years ago, helped address these problems, but finer wires and closer spacing have upped the challenge.
However, recent advances in wire bonding technology have reduced the concern by allowing for wire bonding with insulated wires, a method being introduced by Microbonds in Toronto, Canada.
This new technology obviates wire sweep concerns and could open the door to newer higher productivity solutions in both encapsulation materials and processes.
 | | The Universal AdVantis dispensing platform |
Smaller-Die Challenges
“We are seeing ever-smaller die being underfilled,” says Asymtek’s Adamson, some just 1mm square.
“On PWBs for 1-inch hard drives, the space required for the wetted area around the die is at a premium. With needles you have to leave approximately 1.5mm around the die to ensure that the underfill materials do not wet adjacent components.
“With jetting we can reduce this dimension as small as 0.5mm. If you have, for example, a 7mm square die and have to leave 1.5mm border around it, the die has a footprint on the board of 10mm2. If you pull this in to 8mm2, you are at a 64mm2 footprint. This is almost a 40 percent savings in board area. It’s quite astounding when you look at the numbers how much space you can reclaim,” Adamson observes.
Lead-Free Hinders Innovation
The market will determine if these new materials and techniques offer advantages over the traditional methods, notes Adamson. “Most technologies or methods will find strong supporters the trick is to identify the technology that is going to be adopted by a broad spectrum of companies.
“The EU’s waste electrical and electronic equipment (WEEE) and RoHS initiatives have probably delayed some novel new wafer-level underfill methods, due to higher temperatures required for the no-lead processing. Once we get past the introduction of lead-free processing, I think some of the other approaches such as wafer-level underfill may gain traction.”
Conclusion
More complex chips with greater device density, often with higher I/O counts— coupled with 3D or stacked die/packages configurations—make the precision placement and uniformity of underfills and encapsulants more critical than ever.
Underfills ruggedize the crucial area between chip and substrate (or stacked chip/package). They transform the array of bumps into a virtual monolithic mechanical structure.
The encapsulants provide an essential barrier between the chip and an increasingly chemical-laden atmosphere. Together, they increase packaged device lifetimes.
Do not select any dispensing, encapsulating or molding equipment without first paying close attention to the materials, especially when coping with lead-free solders. The machines are very efficient and getting better.
Be advised that the machines and material sets that worked well with the proven eutectic tin-lead solders may no longer be up to RoHS’ brave new world tasks.
If we’re to be honest, the toughest challenges to efficient underfilling and encapsulating are the onerous, higher-temperature lead-free solder processes dictated by RoHS. Your vendors are indeed aware of the challenges and will work with you to achieve the best results.
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