Leaning the Line Print E-mail
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Written by Chris Munroe   
Friday, 31 October 2008 19:00

How a high-mix EMS firm “waved” goodbye to one soldering machine.

Getting Lean A factor in EPIC Technologies’ adoption of Lean manufacturing principles is to ensure aspects such as floor space and utilization are considered. Eliminating work-in-process (WIP) translates to faster throughput and enhanced scheduling flexibility. In addition, floor space is freed as WIP and inventory are reduced.

However, the company took equipment and floor space optimization one step further by teaming with a wave soldering equipment manufacturer in adapting a comprehensive wave soldering system capable of both lead and Pb-free wave soldering. The result was a duplex wave solution that supports both lead and Pb-free solder processes, while ensuring rapid changeover between the processes. The system architecture adapts to Lean methodologies, saving floor space, utilities and resources.

The duplex wave is a carrier-based system. Unlike board finger conveyors, the machine has a palletized conveyor that requires a carrier to transport product. There are costs associated with the carriers, but to minimize this, universal tooling has been designed for standard PCB array sizes.

The carrier-based system also has a large benefit in that it permits multiple products to be soldered collectively without system changeover. This is extremely important to minimize batch sizing in front of the wave, increasing system utilization and efficiency as a whole. However, with the duplex wave option, this only applies to the solder process currently set up on the system. A switch remains to convert the system from lead to Pb-free and vice-versa. This process takes five to 10 minutes to purge product from the line and exchange wave solder pots. As a result, Pb-free assemblies are run as a batch process.

Each carrier is bar-coded with a unique ID that links to the duplex system for total profile control. A barcode reader on the conveyor signals the machine’s computer to change profiles as different products approach the input. The barcode system also serves as a control point to ensure the correct solder process is selected for the product to be soldered. If the wrong barcode is received, the system will lock down the input and flag the error to the operator, never permitting an incorrect board-profile interaction.

Once the barcode is verified and accepted, and the product enters the machine, flux is applied based on the control settings for the product. The area and volume are predetermined during engineering development with control based on product complexity. The machine offers a dual spray fluxing option to allow users the ability to select a secondary flux type. This feature has not been necessary, as EPIC is utilizing a VOC-free, no-clean flux formula capable of lead, Pb-free, no-clean and water-wash applications.

After flux application, the carbon-based preheat elements are used to heat the assembly to the prescribed topside temperature. An IR pyrometer is used to measure board temperature during preheat. Closed-loop controls automatically adjust heat settings for the product based on IR readings and convection temperatures.

With the duplex wave, only one solder pot is available for production use at a given time. The second wave remains in a liquid standby state outside the conveyance in an enclosed chamber sealed within the main unit. Each solder pot contains a dual wave system, including chip and Lambda operations. Although consistent with standard wave systems, the Lambda wave includes agitation properties to improve solder quality. This agitation permits the Lambda wave to penetrate into selective wave pallets, further enhancing the machine’s ability to selective solder.

Pros and cons. Improving floor space is a major factor in Lean, and it is easy to see the advantage of reducing from two wave systems to support lead and Pb-free production to a single, comprehensive unit.

History also tells us effective utilization of conveyance and carriers can permit multiple wave systems to be consolidated to one. EPIC’s volume production facilities in Juarez, Mexico, run in excess of 20,000 assemblies per day across a single wave. This is not a challenge with an assembly line dedicated to a single product. However, the product mix contains more than 40 different assemblies. With this system, there are zero changeovers because of the conveyance system flexibility. The need for 40 or more changeovers on wave systems of the past would significantly impact operational efficiency.

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The carrier-based configuration also adds the benefit of selective soldering. Masking pallets can be designed to protect sensitive components or masking areas from the solder bath. Tight control on pallet designs and materials have proven successful in wave soldering LCD and sensitive LED technologies, ensuring peak temperature limits are not exceeded on the components.

The added benefit of the masking pallet also adds value for part numbers with tight design constraints. Double-sided SMT and through-hole wave solder can be accomplished with little restriction to the board layout. Top- and bottom-side through-hole soldering can be accomplished with component heights greater than 5.5 mm, and selective soldering of both assembly sides. DfM is made easier through use of masking pallets. Point style selective soldering systems can do the same, but adding processes to an assembly cycle is not always the most feasible solution.

There are materials, environmental and energy savings as well. The benefits of Lean manufacturing can be enhanced significantly when production and engineering teams think outside the box. Partnering and working alongside equipment suppliers can lead to considerable cost benefits over time for manufacturers that drive and implement these improvements.

Chris Munroe is director of engineering at EPIC Technologies (epictech.com); This e-mail address is being protected from spambots. You need JavaScript enabled to view it . His column appears bimonthly.

Last Updated on Friday, 31 October 2008 05:23
 

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