-
- News
- Books
Featured Books
- smt007 Magazine
Latest Issues
Current IssueBox Build
One trend is to add box build and final assembly to your product offering. In this issue, we explore the opportunities and risks of adding system assembly to your service portfolio.
IPC APEX EXPO 2024 Pre-show
This month’s issue devotes its pages to a comprehensive preview of the IPC APEX EXPO 2024 event. Whether your role is technical or business, if you're new-to-the-industry or seasoned veteran, you'll find value throughout this program.
Boost Your Sales
Every part of your business can be evaluated as a process, including your sales funnel. Optimizing your selling process requires a coordinated effort between marketing and sales. In this issue, industry experts in marketing and sales offer their best advice on how to boost your sales efforts.
- Articles
- Columns
Search Console
- Links
- Events
||| MENU - smt007 Magazine
Material Control for Lead-free Manufacturing
December 31, 1969 |Estimated reading time: 12 minutes
Managing the transition to lead-free electronics assembly requires a significant effort in many areas. The challenge does not stop when the new process and materials have been selected and qualified. The key issue that remains is managing the material logistics.
By Francois Monette
A successful lead-free transition requires significant collaborative effort between production, engineering, procurement and component suppliers and distributors. During this process, one area that should not be overlooked is the production floor. The assembly line involves the largest number of people, and the complexity of their task translates to the highest possible risk of errors. This paper focuses on the practical considerations of managing the materials on the production floor during the transition to lead-free.
Managing the Transition
Ultimately, every OEM that designs and distributes electronics products must define its own strategy and action plans for lead-free. This is based on legislation, international markets and other considerations. Many companies continue to assemble leaded products, including products that are exempt from the legislation. Other OEMs will convert all their products to lead-free to minimize the cost and complexity of managing two versions of the same product. As a result, the majority of EMS providers and ODM assemblers will have to manage two sets of materials and run two different processes side-by-side for a significant period of time. Depending on the strategy the assembler will use, this transition can range from a few months to many years in manufacturing, rework and field repairs. In most cases, this will create a logistical nightmare that exceeds the capabilities of current systems and procedures.
The time line of that transition also is sooner than some anticipated. One cell phone manufacturer already has been producing millions of lead-free products in North America over the past two years. Leading producers of PCs also have implemented aggressive schedules with their suppliers to introduce lead-free versions of products. They are doing this up to 18 months ahead of the legislative deadline to avoid additional costs and the complexity associated with running two versions of the same product, or converting these products mid-life.
It is important to realize that these high-volume applications are driving the supply chain. This may become a problem for companies that have decided not to convert to lead-free because their existing parts may be not be available over the next few years. In the end, companies may need to convert their products to lead-free, even if they are exempt from the legislation because some components will be offered only in lead-free versions.
Material Compatibility
Because of material and process compatibility issues, it is critical to avoid mixing leaded components with lead-free components and other materials. On the supplier side, most major component vendors have developed their own roadmap to manage this transition, taking into account the requirements from their various customers. One company* does not recommend forward- or backward-compatible assemblies with their components.
Material Identification
The first challenge is to clearly identify and segregate leaded and lead-free materials. This not only includes components and PCBs, but also solder pastes, solder bars and solder wires. It also may include special tooling that can have subtle differences for both processes, such as stencils. Until now, the major focus has been placed on releasing an industry standard to identify lead-free components and finished assemblies. The NEMI RoHS Transition Task Group worked closely with JEDEC to define a new industry standard - JESD97 “Marking, Symbols, and Labels for Identification of Lead (Pb) Free Assemblies, Components, and Devices.” This provides a standard set of symbols and guidelines for component vendors and assemblers. However, it will not eliminate all confusion because the actual format and content of each label still will vary significantly from one supplier to another (Figures 1 and 2).
Figure 1. Intel lead-free label as it will appear after change.
null
Figure 2. Texas Instruments JEDEC-compliant label with the lead (Pb)-free logo and MSL rating. As of June 1, 2004, TI began shipping lead-free-capable IC components using packing labels that align with JEDEC standards. TI began using a lead-free logo on packing labels in 2003 for devices that use both a lead-free finish and a material set rated for use in lead-free reflow processes. TI’s JEDEC-compliant label will continue to reflect these markings.
null
Part Numbering
Because most procurement and manufacturing systems strictly rely on part numbers, this is an area of concern for material identification. The problem is a lack of agreement of the methods used to manage part numbering for lead-free components in the supply chain. On the user side, NEMI and other groups recommend that lead-free components be identified with new part numbers; and many vendors have agreed to this approach. In some cases, this will take the form of a prefix or suffix added to the existing part number. Other vendors have refused to accommodate this request because it may double the number of part numbers that they must manage. In some cases, it may exceed the capability of existing systems. In this case, the transition will be managed by production date or lot codes.
The actual method being used to identify lead-free components should be defined clearly and communicated to assemblers through standard Process Change Notice (PCN) procedures. The ultimate responsibility of managing this variability resides with assemblers.
Automating Material Control
There is no general industry standard on component and material labeling. This means that every vendor has its own internal labeling format containing different elements of information. Typically, this includes a part number, lot number or date code and quantity. The information generally is printed in a readable form with certain fields also available in barcode or 2-D matrix formats.
This poses a challenge when assemblers try to automate the control of materials in the warehouse and on the production floor. A limited number of large OEMs can specify their own barcode label formats to all suppliers. However, the majority of assemblers must generate their own barcode label for each batch of material upon receiving or kitting - before it is released to production.
Figure 3. Manual scanning of a barcode label.
Consequently, we are dealing with a closed system and a uniform labeling scheme, the most effective approach is to assign a unique serial number to each individual item. Then all the material and process information assigned to this specific item can be maintained and updated in a central database. The serial number is generated when the material is received, or before it gets released to production. This unique number can be printed as a simple barcode, or it can be assigned to an RFID tag that is temporarily attached to the material container. This identifier can be scanned quickly while materials move from one location to another in the factory, on and off production equipment, or in and out of a storage location (Figure 3). To speed up the process, individual machine and storage locations also can be identified with a unique barcode label. The operator scans the material and its location to perform a transaction in the material control system. Using RFID tags and RF antennas integrated into production equipment and storage locations further automates the data acquisition process (Figure 4). This has several benefits, one of which is an accurate real-time inventory of all materials on and off the assembly line. It also provides the foundation for other material control applications such as line setup validation, MSD control and traceability.
Figure 4. RFID smart feeders on placement machines.
null
Moisture-sensitive Components
There is a subset of electronic components that presents assemblers with a logistical challenge. The majority of active components that are packaged with plastic and other organic materials are categorized as moisture-sensitive. This means that they must be packaged and shipped in sealed dry bags with labels indicating that they have a limited floor life once the bags are opened. The actual floor life varies from a few hours to a year, and it changes based on the history of exposure time in various environments. This requires a high level of component tracking on the shop floor.
The introduction of lead-free has created a major impact on moisture-sensitive parts. The higher reflow temperature translates in higher internal pressure, reducing the allowable floor life. This means that the manufacturer needs to re-test and re-classify all components. Studies have shown that this can result in downgrading components by one to three levels of moisture sensitivity.
Other components that were not previously considered as moisture-sensitive now must be handled with similar precautions. This includes certain types of passives, connectors and PC boards that can suffer damage through a combination of exposure to moisture followed by high-temperature reflow. In addition to traditional cracks and internal delaminations, new failure modes also have been reported for PBGAs. Excessive warpage of large-body components has been influenced by moisture. This failure mode will be included in the upcoming release of the MSD industry standards.
Because the same parts can be used by different customers in Sn/Pb and lead-free assemblies, some component vendors have decided to indicate different MS levels at two different reflow temperatures. This dual-classification method is technically justified, but increases the complexity of information on the label and the risk of human errors during assembly. MSD control is frequently compared to ESD control from 10 years ago. Without considering lead-free, most assembly operations do not comply fully with the industry standard and routinely expose their ICs to excessive stresses during reflow. The transition to lead-free will compound this issue by reducing process windows and increasing the rate of field failures due to internal component damage.
The same types of automated material-control systems that have been used by leading assemblers to control moisture-sensitive components are becoming a necessity for anyone assembling lead-free products. Existing systems and procedures must be upgraded to deal with the new elements associated with higher reflow temperatures.
Line Setup Validation
Another common production task is validating setup of each machine on the assembly line. Previously, this has created some issues because production operators must work with a large number of differing elements. The tendency to make mistakes and load a material in the wrong location increases. Loading the wrong reel of components on a placement machine can result in thousands of defective assemblies. With the introduction of lead-free, the complexity level and risk of human errors increase greatly.
Manual Setup Validation - Clearly written instructions and setup sheets are needed. These often are combined with an additional verification process and may include a complete first article test and inspection, or having a second operator or quality control inspector verify the setup of every machine prior to production. Both methods translate to assembly line downtime, and are prone to human errors.
Semi-automatic Setup Validation - The most common method of automated setup validation is using barcode labels on material containers. A typical solution for placement machines will consist of scanning a barcode label on the reel of components, then scanning another barcode label on the feeder or feeder slot on the placement machine. This data is compared with the specified machine setup and discrepancies are identified.
Closed-loop Setup Validation - This is the highest level of validation and involves a type of intelligent tooling, such as a smart feeder. In this method, a reel is associated with a smart feeder during an offline feeder setup process. When the feeder is loaded onto the machine, the system automatically detects and validates that the correct feeder and component are loaded in the correct location.
Figure 5. RF antenna for a solder-paste jar.
Replacing RFID tags with barcode labels also can provide a way to obtain fully closed-loop setup validation on any type of material. For example, closed-loop validation can be retrofitted on an existing screen printer. A low-cost reusable RFID tag is attached to each stencil and solder-paste jar when they are loaded in place (Figure 5). The system requires no operator intervention unless a setup error is detected. This higher level of automation, however, requires a higher investment in terms of hardware. The cost often is offset by the elimination of manual scanning and the associated errors. Ultimately, a complete validation setup system should be flexible enough to support all types of materials and equipment.
Traceability and Material Declarations
Manufacturing and material traceability has been the subject of increased industry attention. Many OEMs have asked suppliers to provide component-lot traceability data for every product, on every board. Individual boards are serialized to provide a finer level of traceability. The main drivers for this have been the need to precisely identify the root cause of a specific defect in the field, and to enable selective recalls of other products that may have the same problem.
The transition to lead-free increases the focus on material and process traceability. Lead-free legislation and customer requirements will mandate assemblers to provide documented evidence that a specific product was built with lead-free materials. As a result, component lot traceability no longer is sufficient for many customers. Some leading OEMs are requesting complete process traceability for every board their suppliers assemble. To support lead-free compliance, this data also should include the part number’s lot number or date code and other relevant information to identify that respective suppliers have classified all materials as lead-free.
Efforts are under way to standardize the process for gathering and reporting material content. A Joint Industry Material Composition Declaration Guide is being developed. For assemblers, this translates into a significant effort to obtain the material content of each component on the bill of materials (BOM) for every product. Assemblers then must generate the material declarations for the finished product.
There is a liability aspect associated with lead-free legislation and material traceability. Although there is real cost involved in capturing and storing this data, the alternative could be worse. The good news with material traceability is that the same material control system used to manage inventory on the shop floor, prevent setup errors and provide MSD control also can be used to record and associate materials with finished products. This provides a new level of information beyond traditional component-lot traceability. The system can be cost-justified on the basis of actual improvements in setup time and reduced scrap and rework. It does not need to be seen as an additional expense required only for gathering data. It becomes part of an integral material-control system focused on reducing waste by insuring that all the right materials are at the right place at the right time.
Conclusion
Once lead-free materials have been selected and the process has been qualified, the manufacturing issue of managing material logistics remains. There are critical aspects of controlling materials on the production floor, including identifying and segregating Sn/Pb and lead-free materials, validating line setup, controlling moisture-sensitive components and providing complete material and process traceability. These issues can be addressed with proven and cost-effective material control systems - using a combination of barcode and RFID technology.
* Intel
References
For a list of references, contact the author.
Francois Monette, vice president of sales and marketing, Cogiscan, Inc., may be contacted at (450) 534-2644; e-mail: fmonette@cogiscan.com.