The industry drive towards lead free, or so-called "Green" electronic products is building momentum. Dating back to the 1990's, and proposed legislation in the U.S., it is now European Commission Directives, Japanese legislation, and market pressure that are forcing implementation. It is the marketing of environmentally friendly products by Japanese OEM's that is applying pressure throughout the entire industry to keep pace. As Europe prepares to meet the EC Directives expected to be in force July 2006, the level of conversion to Green semiconductor packaging is sure to increase. Even in the U.S., which has no pending legislation to ban Pb, there has been an Act introduced in Congress to spur activity for the recycling of electronic products. The Computer Hazardous Waste Infrastructure Programs (CHIP) is currently under consideration. It is intended to provide grants to companies researching technology to reclaim and recycle electronic waste that would otherwise end up in a landfill. The "Green" electronics movement is truly a worldwide phenomenon. Amkor is fully committed, and prepared, to meet the needs of our customers in this dynamic environment. rohs

From an IC packaging standpoint, what does it take to be Green?

The legislation and directives mainly focus on two issues, the elimination of certain elements and compounds, and the recycling of products at "end of life". For semiconductor assembly it is the elimination of these banned materials (Shown below) that is the primary effort. First, Lead (Pb) must be removed from package terminations, plating finish and solder balls. Although potentially exempted from the ban, development of Pb free alternatives for solder die attach materials and flip chip interconnections are also under way. The second group of banned materials is brominated flame retardant compounds used in mold compounds and substrates for laminate packages. Poly brominated diphenyl (PBB), poly brominated diphenyl ether (PBDE), and their derivatives, are the targeted chemicals. Associated with the halogenated compounds are the antimony oxides that form a synergistic relationship to aid in flame suppression. Although not specifically banned, Amkor considers removal of antimony necessary for making a package Green.

The maximum levels of these materials allowed in a Green package are still undetermined. However, there are industry efforts underway to establish specifications. In the meantime, Amkor is operating under the premise that if none of the targeted materials were intentionally added during their manufacture, then they qualify as Pb or halogen free. Minor impurity levels that exist due to limitations in purification technology are deemed acceptable by current industry thinking. On an interim basis, Amkor has established some guidelines. For Pb free requirements, the solder materials used must contain no more than 1000 ppm of Pb. For halogens, chlorine and bromine must each be less than 900 ppm. The same limit of 900 ppm applies for antimony.

How does this impact IC packaging?

The elimination of these elements and compounds will have quite a profound impact on the semiconductor packaging industry. Many existing assembly materials can no longer be used because they contain one or more of the banned substances. In addition, materials that do not contain any of the banned substances may be excluded because they cannot meet the increased board assembly and reliability requirements. These are a direct result of the higher reflow temperatures required by the new Pb free solders. Packaging materials are designed to meet very strict reliability and performance requirements. The required changes to the material formulation, coupled with the need for a performance increase, translate to a total redesign of IC packages. The table below indicates the packaging material changes that are required for Green packages.

Solutions for the elimination of Pb

The most common of the solder alloys proposed for Pb free assemblies are ternary combinations of tin, silver and copper. These alloys typically contain 3 - 4% silver, 0.5 - 1.0% copper, with the remainder being tin. With melting ranges just below 220°C, versus eutectic tin/lead at 183°C, packages must be able to survive much higher temperatures during reflow assembly processing. Despite these more severe temperature exposures, the ternary Sn/Ag/Cu alloys are being used successfully in production. As a result, they are a natural choice to be used for solder balls on area array packages. In 2000 Amkor announced adoption of the Sn/4.0Ag/0.5Cu alloy as our standard material. This was done after completing board level reliability testing, characterization of the ball attach process, and cooperative efforts with industry consortiums. Since this announcement, Amkor has qualified numerous packages with this Pb free alloy. In 2001, Amkor also started a program to characterize and qualify the Sn/3.0Ag/0.5Cu alloy. This alloy was added to our qualified Pb free materials to meet the requests of the Japanese market.

Terminations for leadframe packages have historically been plated with a tin/lead solder of various compositions, typically in the range of 80 - 90% tin. Removal of the Pb from the package termination is not nearly as straightforward as with the solder balls for area array packages. The simplest solution would appear to be a pure Sn coating. Deposition processes are readily available, cost efficient, and a tin finish is compatible with both Pb free and tin/lead soldering processes. However, reliability concerns about tin whiskers is preventing universal acceptance of this solution.

Another viable option, with a long history in the industry, is nickel-palladium pre-plated leadframes. Available for more than 10 years now, this Pb free finish has not gained widespread acceptance. However, The Japanese electronics industry has used a higher percentage of these packages that any other market segment.

Tin based coatings with a small amount of a non-lead metallic additive are also being considered as substitutes for lead based solders. Tin/bismuth, tin / copper and tin/silver are the most common options under consideration. Ternary-based coatings are not as viable due to the inherent problems with the deposition processes. Of these options, tin / bismuth has been adopted by a number of companies, mostly in the Japanese market.

To service our wide range of customer needs, Amkor offers three Pb free choices for leadframe package terminations, nickel-palladium with a gold flash, tin / bismuth (nominal 2% bismuth), and a pure matte tin finish.

For flip chip applications, Amkor has researched a number of different solutions. First of these is a straightforward replacement of the standard tin/lead bump with a Pb free alloy, Sn/Ag/Cu or other similar alloy. The second option is a gold stud bumped die, that would then be attached to the substrate with either Sn/Ag solder or an ACF (Anisotropic Conductive Film).

Package reliability solutions

Reliability requirements are being pushed to limit for Green electronic assemblies. Board assembly reflow processes are now required to maintain peak temperatures of 240 - 260°C. This can be as much as 20 - 40°C higher than current processes. Creating a package that resists delamination under the added thermal and mechanical stresses calls for a new breed of materials. Amkor has worked extensively with our material suppliers to develop and characterize these materials. We have a full line of packages that meet, or surpass, a JEDEC Level 3 moisture resistance at 260°C. Mold compounds, die attach materials, leadframes and substrates working together to maintain package integrity with improved adhesive and moisture absorption properties.

Additional Information:

Description	File Type	File Size
Green Packaging Services Sheet		687 kb
Green Packaging Services Sheet   (Japanese Translation)		100 kb
Amkor Definition of “Green” IC Packages		20 kb
White Paper: "Reliability of Lead-Free Solder   Connections for Area-Array Packages		600 kb
Lead-Free Soldering Technology Centre (SOLDERTEC) - www.lead-free.org

For more information on Green / Pb-Free Packaging please contact an Amkor Regional Sales Office near you, contact your Account Manager or fill out a Request for Additional Information.