Machine versatility: aspects to evaluate when considering customization.

Versatility, or the ability to address different requirements with the same method or hardware, is a critical differentiator for most production facilities. When purchasing screen-printing equipment, consider the process requirements that dictate the level of the machines' versatility.

Several non-solder paste printing applications, such as printing adhesives for bottom-side component attachment, are understood and widely used. Some custom application evaluations require process investigation while others require investigation into the equipment's capability to perform it. Some require both process and equipment capability analyses.

The process evaluation investigation of a custom application is always unique to that application and includes tasks such as stencil or screen design, material printing process, environmental considerations, tooling requirements, product handling or presentation to the print head. A good deal of the custom application evaluation focuses on equipment versatility. This can be considered in two areas.

* Versatility in traditional solder paste printing applications.

* Versatility in custom printing applications.

Operations Change

When evaluating equipment versatility in traditional paste printing applications, consider the level of versatility needed for current and future applications. Equipment versatility requirements are less for a dedicated manufacturer of one particular product than those of the operation that builds a variety of products. However, dedicated, high-volume operations often eventually change products or transfer equipment from sites where the printer versatility requirements are more demanding.

A basic machine versatility consideration would be the size of the boards to be built. If building 6 x 8" boards today, we would not purchase printers that could only process a maximum size of 6 x 8" because of the likelihood that we will soon be building larger ones. For traditional solder paste printing applications consider equipment versatility factors such as:

* Board thickness.

* Cycle time. This is a detailed understanding of the entire printing process cycle time including all overhead functions (stencil wiping, post-print inspection, solder paste dispensing onto the stencil, etc.)

* Process setup. The ability to set up the equipment quickly, including support-tooling change.

* Post-print inspection. Will 2-D post-print inspection be needed and if so how fast will it have to be? Some customers may demand 2-D inspection that can inspect every solder paste print at line speeds.

* Alignment precision. For boards with miniature components such as 01005, the precision of the board-to-stencil alignment requirement will be more demanding.

* Printing type 4, type 5 or even type 6 solder pastes. Recent studies have indicated that smaller powder sizes may be required for miniature components.

* Traceability. RoHS compliance is accelerating the drive for equipment that can trace specific product to specific manufacturing conditions (date, material, operator, quality information, etc.).

* Process setup verification. The ability of the equipment to recognize and verify all of its inputs (solder paste, stencil, tooling, program, etc.) prior to processing the first board.

* Print head changeover. The equipment's ability to be quickly and easily changed from enclosed print head to squeegee blade, based on the product.

* Substrate support techniques. Can the machine effectively provide support for the custom application, and does it offer easy transition for other products?

* User interface. Printing equipment is used all over the world and often transferred by customers from country to country. The user interface must be intuitive and easy to learn and use to minimize language and training issues.

For custom applications, aspects to consider include:

* Adhesive printing. The most common application for adhesive printing is attachment of bottom-side SMT components in a mixed technology product.

* Epoxy, ink and flux printing. There are many applications for printing these materials on a variety of substrates.

* Printing on a non-flat surface. We recently worked with a customer on printing a conductive epoxy on the rear surface of a concave mirror.

* Printing with silkscreens. Silkscreen printing is required in many custom-printing applications. Often the printed material thickness requirement can only be achieved using a silkscreen.

* Transport and alignment system. Custom applications may require printing on ceramic, glass, wafers or other material. The transport and alignment system must be capable of handling these substrate materials.

* Wafer printing. A technology for bumping wafers for flip-chip applications.

Having maximum versatility in printing equipment optimizes the support of as many applications--be they traditional solder paste printing or custom applications--as possible.

Joe Belmonte is project manager, advanced process development, at Speedline Technologies (speedlinetech.com); [e-mail]. His column appears semimonthly.

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