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A case study of how one EMS company made the switch.

The impact of producing RoHS-compliant parts is significant. Risks for not producing compliant parts include an inability to sell to customers in Europe after the deadline, and possibly an inability to sell components to any customers in the future. Considering the difficulties involved in producing both standard and RoHS-compliant parts within a particular plant, many industry leaders believe the entire market will eventually produce only RoHS-compliant electronics.

Such challenges should prompt EMS customers to re-evaluate their partners and select a supplier that has invested the capital and the time to competently and consistently meet the needs of customers who require RoHS compliance. For organizations currently building PCBs in-house, the transition to RoHS compliance can be significantly easier and less expensive if outsourced.

A typical circuit board contains several of the substances banned by RoHS, including lead, cadmium, PBB and PBDE. When faced with the need to be RoHS-compliant by July 2006, SMC had several challenging issues to manage. The company needed to first find Pb-free alternative materials for traditional SnPb plating as well as soldering. At the same time, engineers worked toward effectively managing material and component changes from suppliers while setting up manufacturing systems that keep standard products separated from RoHS-compliant products.

Documentation and certification were additional challenges. At every point in the channel, RoHS compliance must be certified as electronics parts pass between plants. All raw materials, including electronics, labels, test marks, screws, brackets and wires, must be compliant. It took a year for SMC engineers to master the learning curve involved with defining processes, purchasing equipment, creating documentation and training employees to meet customer demands for producible, functional, RoHS-compliant assemblies.

Successful management of the RoHS-compliant initiative requires engineers from both the OEM and the EMS provider to work together to identify RoHS-compliant substitute parts in existing and new assemblies. In the early months of the transition, parts availability is the most significant challenge for all parties involved. Component materials may need to be changed not only because of the necessity of producing RoHS-compliant parts, but also because existing materials may not be able to bear the higher heat required to solder components in a Pb-free process.

In 2005, SMC purchased three licenses for the Arrow Electronics database, which enables customer engineers to assist in the identification and procurement of alternative environmentally compliant parts for use in their assemblies. Depending on component availability, the customer may need to wait several months for finished products, or the customer might redesign the assembly using RoHS-compliant parts currently on the market.

Early in 2005, the IT group at SMC redesigned the company's internal component database to identify and sort RoHS-compliant materials. Parts come into the system on reels, in trays, in stick form, in bulk or in bags, and are immediately labeled with internal part numbers that begin with the prefix of "G" (green). Prior to assembly, parts are stored in vertical storage units (VSUs) to simplify identification and to effectively separate and accurately pull inventory.

Orders are entered into the system as total assemblies with an assembly part number. With RoHS-compliant orders, green move tickets travel with batches of assemblies through the system (Figure 2), creating a high visual impact and further ensuring separation of these orders. Work instructions are color-coded to help workers differentiate between assemblies during manufacturing. Work instructions and control documents have been updated to comply with ISO and RoHS requirements.

Click here to see Figures 2 and 3 (56KB PDF).

As parts to be used in RoHS-compliant assemblies come into the SMC plant, operators are required to verify and document compliance. Some suppliers are transitioning to Pb-free without changing part numbers, which makes component tracking, dating and marking especially critical within the plant.

To ensure that parts are RoHS-compliant, SMC uses a diagnostic spectrum analyzer to chemically test samples from batches of parts. The quality assurance department also verifies compliance through visual inspection of samples taken at different points in the process. SMC ships certificates of compliance (Figure 3) to its customers with their orders, as specified by the customer. Documentation requirements differ for individual countries and states, ranging from a BoM that lists only the part numbers of components to a lengthy document that lists details of each component that is part of the final assembly.

To eliminate lead and other hazardous substances from PCBs, SMC engineers have changed materials and altered the design process within several areas of the plant.

Traditionally, incoming bare boards are coated with a SnPb material that incorporates a bromine flame retardant. The choice of alternative laminate materials for RoHS-compliant boards depends on the method of soldering and the amount of heat applied during the manufacturing process. RoHS-compliant options include HASL, ENIG (gold), immersion silver, organic solderability protectants and immersion tin. The Pb-based ink used to screen-print bare boards prior to assembly must also be substituted with a non-leaded ink.

In the first assembly step, Pb-free solder paste is applied with a squeegee to specific areas of the board via a custom stencil. The majority of parts are then placed on the board by a component placement machine. Operators then inspect each assembly, attach hand-mounted parts and send the board into the reflow oven.

In 2005, SMC purchased four new reflow ovens to handle RoHS-compliant assemblies. In the reflow ovens, the board and paste are slowly heated and cooled on a conveyor belt that runs through a long oven that is split into a number of zones. RoHS-compliant assemblies require the reflow oven to be set at 220°F, compared with 186°F for traditional leaded assemblies. This higher temperature makes the process window tighter, and Pb-free solder does not flow and adhere as well to the board.

Next, if the assembly includes through-hole components, those parts are placed on the board and sent through the wave solder machine. The machine applies flux to the top of the board and solder to the bottom of the board, heating the assembly to 250°F to adhere the through-hole components. Since the wave solder machine is shared between RoHS-compliant production and regular SnPb production, two pots of solder are kept completely separate in this area of the plant. Between orders of the two types of assemblies, the wave solder machine is completely cleaned. Materials and soldering irons are stored separately as well.

In the final phase of manufacturing, boards are inspected and washed with deionized water. Each circuit board is inspected by AOI, which checks the security of each joint and pinpoints areas that require hand soldering touchup. For boards that include more sophisticated electronics, such as BGAs, a higher resolution x-ray imaging machine is used during this final inspection step. If hand soldering is necessary, an operator uses Pb-free solder to adhere the parts just before final inspection and functional testing.

Prior to the transition to RoHS-compliant assemblies, SMC operators were trained to manage the new RoHS-compliant process in accordance with IPC-A-610D for manufacturing electronics assemblies. Since Pb-free solder does not wick and flow as well as SnPb, operators were trained to not only meet technical requirements, but also to recognize acceptable soldering at each point in the manufacturing process. A trainer leads operators through two weeks of half-day classes, ending with a written test that affirms their readiness to handle Pb-free processing.

The challenges of producing RoHS-compliant parts in the EMS industry are significant, with many issues related SMC employees have worked to master the many issues related to sourcing RoHS-compliant components, purchasing new equipment and implementing separate manufacturing processes. On the management side, document control measures must be carefully implemented, operators have been thoroughly trained and customers have been initiated into the new systems and methods of RoHS compliance.

Don Taylor is customer engineering manager at SMC (smcems.com); dtaylor@smcems.com.