Pb-Free Status and Plans

Lead (Pb) is a naturally occurring element used within the electronics industry primarily to enhance soldering of semiconductor product’s external pins or terminals onto PC or PW boards. It’s been used for many years as the most consistent method to allow soldering without the need for extremely high solder melting temperatures that could damage components or the board itself. However, most world health organizations consider these materials to be hazardous substances, which have already been removed from many products over the past years (i.e., paints, soldering of copper water pipes, tin can soldering, etc). The U. S. electronic interconnection industry has calculated that it uses less than 2% of the world’s annual lead consumption (estimated at >10K tons). All currently available scientific evidence and U. S. government reports indicate that the Pb used in PC/PW board manufacturing and electronic assembly produces no significant environmental or health hazards.

While there is no current prohibition of its use in the electronics industry by the U. S. government, Europe and Japan are in the process of banning Pb and many other hazardous substances by July 1, 2006. That is being required by the RoHS Directive (Restriction on Hazardous Substances) issued by the EU, which bans the use of Pb (use in some applications will be exempted until 2010), Cadmium, Hexavalent Chromium, PBB and PBDE. Some states in the U.S., such as California, have announced they will enact RoHS in January of 2007. As the world moves forward to reduce or eliminate environmentally hazardous materials, it’s become clear that the semiconductor industry must eliminate the use of lead in the terminal coatings used to facilitate soldering PC and PW boards. A product is considered Pb-free if it has less than 0.1% Pb by weight in homogeneous materials, and where none has been intentionally added as part of the manufacturing process. Our industry also plans to remove other hazardous materials that may be used in the processing or manufacturing of products. Specifically, the flame-retardant materials Antimony Trioxide (Sb2O3) and Bromine (TBBP-A) used in epoxy mold compounds; and TBTO in marking ink (already eliminated).

The problem for several years was that there’s been no mutually agreed-upon standard for an acceptable substitute material to both the semiconductor industry and OEM companies. Suggested alternatives that have been qualified by a number of companies are: 100% Matte Sn, Sn/Bi, Sn/Zn/Bi, Sn/Zn/Al, Sn/Ag, Sn/Ag/Cu, Sn/Ag/Zn, etc. There are almost as many methods and combinations being looked at as there are companies doing these evaluations. All can be made to work, but not always with the same results. For the board mounting industry, receiving similar product from suppliers using different terminal plating materials with varying melting temperatures could cause chaos within their soldering operations.
Everyone has been looking for a consensus on the best material or material combinations to use. While there is no single industry accepted substitute, there are three leading contenders to replace current Sn/Pb solder plating: 100% Sn, Sn/Bi and Sn/Ag/Cu.

There have been numerous industry concerns over Sn “whisker” growth on plated terminals, an affect caused by creation of elongated single crystals of pure tin that can grow up to 2 mm in length and up to 3 mm in diameter. These conductive whiskers can grow spontaneously without applied electrical current or even moisture, and they are independent of atmospheric pressure (they can grow in a vacuum). Their appearance can be straight or curved, and the outer surface is usually striated. They can start appearing shortly after plating or take years to appear. While no widely accepted single factor explains the exact mechanism, it’s primarily been attributed to stresses in the tin plating itself. That can be due to the actual plating process, formation of intermetallic compounds (within the tin grain boundaries), bending or stretching of plated surface, or scratches in the plating from handling or equipment.

The newer plating processes and equipment used by our suppliers has significantly reduced or eliminated the risk of Sn whisker growth on package terminals. Our assembly suppliers have all performed extensive tests and monitors, trying to determine if Sn whisker growth could be created. None have been found so far, and they continue to monitor their process to insure they will not occur. A remaining concern might be that there is still no industry-accepted test method for determining how Sn whiskers grow on a plated surface. It’s our belief that the current matte Sn plating material and process being used is more than sufficient to avoid the potential risk of Sn whisker growth on IC package terminals. However, in order to assure that fact Pericom has also implemented a post-Sn plating one-hour bake at 150°C with each of our suppliers. Based on a number of industry studies it’s believed that will relieve any stress that could cause whisker growth. Another possible solution now gaining favor is use of nickel underplate; that process is still being considered as an alternative.

Along with removing Pb from semiconductor packages is the elimination of other hazardous chemicals/materials that are or will be banned by most countries. Two types of most concern are Antimony Trioxide (Sb2O3) and Bromine (TBBP-A), used as flame-retardants in epoxy mold compounds. Other alternative materials have been developed by the mold compound manufacturers, and are being evaluated by both Pericom and our subcontract suppliers. In most cases, we are attempting to replace both the Pb and the current flame-retardants at the same time. An initial attempt by one mold compound manufacture to use a particled phosphorus agent was found to have reliability problems and withdrawn from the market. Pericom never used that substitute material in any of our packages. New materials are still being evaluated, and Pericom will only use those proven to have no issues before allowing any conversion that will permanently eliminate Sb and Br. Removal of TBTO from marking ink has been completed, with Markem having removed it from their inks effective October 2002. Products manufactured after that time will have no TBTO in the mark ink.

There is currently no industry standard for how Pb-free and/or Green products shall be marked so that it can be distinguished from non-environmentally acceptable material. Until there is a standard, Pericom has chosen to mark all it’s product (where space on the package surface permits) with an “E” to designate Pb-free and/or Green. This letter will be marked after the complete part number. Where package space does not permit, there will be a “dash” above the first character of the device type to signify Pb-free product. Pericom will advise customers through the applicable datasheet or on our website as to the appropriate method used to identify environmentally safe products.

TBA

Active Element: This is usually defined as the silicon chip (or die), which can be doped with extremely small quantities of arsenic, boron, phosphorus, etc. as part of the wafer fabrication process. The metallization connecting the transistor circuitry consists of two or more thin layers of aluminum, with small amounts of titanium and/or titanium/tungsten. The chips are then bonded to a leadframe or substrate paddle area using a silver-filled epoxy. Gold wires then bond the chip to the leadframe/substrate’s terminals outside the encapsulated area.

Leadframe or Substrate (BGA):For electrical connection, a Cu alloy is used for leadframe packages, with spot silver plating in the die paddle area. The external pins are then plated with 85% Sn/15% Pb for current packages. BGA package types most often use multi-layer laminate material (such as FR-4) and solder balls (63%Sn/37%Pb) as the external terminal connection.

Package: The IC chip is shielded from the outside environment by an epoxy resin encapsulant, with up to 70% quartz particles. Antimony trioxide (<1.6%), and Brominated epoxy resins (<1%) are currently used as flame-retardants to meet UL94-V0 requirements for all Pericom package types.

Antimony Trioxide: (Sb2O3, CAS-No. 7440-36-0): A white, odorless, fine powder which is used as a flame retardant as well as pigment, catalyst, chemical intermediate, and lubricant.

TBBPA: (Tetrabromobisphenol-A, C₁₂H₁₂BR₄O₂, CAS-No. 79-94-7) a Brominated Flame Retardant (BFR), which is currently the largest volume BFR in production today.