SMART Group

Printing has moved from an art to a science based on the work of leading suppliers in co-operation with industry. Much of the work of the NPL has provided a scientific basis with a better understanding of material properties and printing equipment. There are the traditional processes where printing is used but where else can printing be used in electronic assembly. The opening presentation will illustrate the total assembly process and show where printing is an option, or where it may be used in the future.

An Accurate And Robust Measurement Methods For Characterising Solder Paste
Milos Dusek, NPL

Solder paste measurements are essential in product development, SPC and quality control. A technique has been developed that fully characterises the deposits, providing height, volume and defect level. The advantage of the algorithm is in its robustness, which can accommodate unlevelled surfaces, rotated or mispositioned samples or even measurement noise. How defects occur will be shown with under-stencil camera video-sequences.

Comparison of enclosed and squeegee systems for fine pitch printing
Chris Hunt, NPL

Enclosed print heads are now widely used, work at NPL has studied their performance, and these results will be discussed, and will include fine pitch (300 µm) printing, the effect intermittent printing over a 5 day period, the effect of temperature, and the effect of distorted substrates

Analysis of the SMT Stencil printing process relating to small features
Bruce Seaton, Speedline Technologies

As components become increasingly smaller, the stencil printing process is once again challenged. What do we need to do to develop and keep our solder paste printing process in control for 0201 and 0.5mm pitch CSP. Breaking the technology barrier!

Effect of metal content and particle size on printing
Ling Zou, NPL

The role solder paste properties on the printability of solder paste will be discussed. The effect of solder composition and metal particle size on the quality of fine pitch stencil printing is discussed. The influence on print quality and other factors such as the incidence of solder balling are presented.
Solder paste for wafer bumping

Steve Dowds, Indium Corporation
As components such as CSPs become still smaller, conventional ball placement operations become very expensive. Using solder paste for this application is very attractive due to the potentially very high throughput and low cost. However, wafer bumping at 100-150mm pitch (0.004-0.006") is very challenging, particularly in terms of printing. This presentation examines the prospects for this process.

Design for Printing Through Hole Reflow
Bob Willis, SMART Group

Through hole, Intrusive, Selective, Spot Reflow are all terms to describe a process of eliminating selective soldering, wave soldering or manual soldering operations. The reflow of through hole components reduces cost, eliminates equipment and is a simple process to implement. The printing process and the correct stencil technology can provide all these benefits and more if considered in detail. This presentation will look at the design issues for effective paste application and how the printing process and stencil design can produce solder joints with the same reliability as traditional techniques.

Approaches for stencil printing conductive and non-conductive adhesives
Martin Wickham, NPL

The stencil printing of wave soldering adhesives is on the increase as end users strive to improve the productivity of mixed technology assemblies. Add to this the potential of conductive adhesives as a lead-free replacement and the interest in using stencil printing for non-solder paste applications is on the up. This presentation covers recent work jointly funded by DTI and UK industry, to characterise the printing of both wave-solder and conductive adhesives.

Pump printing, and application examples
Alan Hobby, DEK

In spite of all predictions, wave soldering is still alive and well. When the wave is fronted by a high-speed component placer, a high speed glue deposition machine is also needed. Stencil printing has the potential to be an extremely high-speed process. When coupled with thick stencils, many of the perceived limitations of stencilling are eliminated. Now, more interestingly, these same thick stencils have been adapted to print solder paste in some previously impossible situations."

Pitfalls and best practice for dispensing
Alan Brewin, NPL

A NPL code of practice for dispensing of electronics materials has just been released. This presentation highlights some of the hints and tips, justified with practical data, resulting from dispensing trials. Solder paste, surface mount adhesive, conductive adhesive, glob tops and underfill materials are included.

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