Recently we spoke to Mark Flaskett, Product Manager - Printing, for Mycronic PCB Assembly.
Mycronic is a global high-tech company that develops, manufactures and markets production equipment that meets the electronics industry's high demands for precision, flexibility and efficiency.
Jet printing of solder paste has established itself as an essential process for manufacturers of high-reliability electronics with a high-mix production.
Due to the advancing development in electronics production, traditional stencil printing is becoming an even greater challenge. Miniaturization is seen as the key to the future of automation, and translates into a constant reduction in stencil apertures and paste deposit volumes, as well as distances between components.
The quality of stencil printing depends on many different factors. Only a perfect interaction between stencil, paste, completely flat PCB and solder resist, together with coordinated printing parameters, can ensure optimum print quality.
Stencil printing is a well-established and reliable process but its dependence on a wide range of parameters generally makes it quite inflexible. In addition, smaller stencil apertures for miniaturized components worsen the Area Aperture Ratio (AAR), i.e. the ratio of aperture surface to the aperture wall surface.
This ratio is of significant importance for the solder paste transfer efficiency, resulting in reduced print quality for fine pitch applications and a more unstable printing process.
This illustration shows significant effect of solder paste entrapment in a stencil when stencil is too thick.
Solder paste printing without stencil
Mycronic MY700 Jet Printer offers an option here that eliminates the need for a stencil: piezo printing technology enables stencil-free and contactless solder paste application, in which small drops of solder paste are printed onto the circuit board under 3g acceleration.
Mycronic MY700 Jet Printer consists of the ejector – the print head – , the machine with high-speed and high-precision gantry system, and the programming software. The heart of the system is the ejector unit. The plug-and-play design allows an easy and quick insertion of the cartridge, and the dot size can be adjusted.
Up to two print heads are available in the machine. The MY700 Jet Printer has linear drives in X&Y, featuring an axis acceleration of up to 3g.
Dot size ranges from 210 µm up to 640 µm, according to the ejector and solder paste used. Mycronic MY700 can jet at a top speed of 1,080,000 dots per hour, with 35 µm repeatability at 3 σ. Such precision and repeatability performances enable to jet paste for components with the smallest package or pitch size.
With an extremely precise “on-the-fly” solder paste printing process, optimal solder joints of any shape and size can be guaranteed. The program creation takes about five minutes. First, CAD data is imported, then the pads and component shapes are automatically generated.
If necessary, fine-tuning is carried out, then the program is published. The technology could be compared to printing a document on an inkjet printer: the printing program is prepared off-line from the CAD or Gerber data for a particular PCB and then sent to a jet printer for printing as many “copies” as required.
More design freedom with jet printing
From pin-in-paste to package-on-package, flexible substrates and board cavities, the Jet Printer handles all these jobs with total control of solder paste deposit size, volume, shape and position with micrometer accuracy.
Since the process is completely controlled by software, the solder paste volumes can be altered ‘on-demand’. The jet printing process enables precise control of solder paste deposits in three dimensions (3D). It is possible to fine-tune the volume, area coverage, height and layers of solder paste that need to be applied to every individual pad, component and package, as shown on the pictures hereafter.
Unlike stencil printing, jet printing offers the possibility to adjust the amount of paste and the thickness of the deposit to the exact needs of every single component from the same PCB, without having to comply with “keep-out distances” as for stepped stencils. This opens new perspectives for electronics designers looking to shrink their PCB size, or to integrate more diverse components without enlarging the PCB.
As an example, with jet printing it is possible to print pads for components with pitches as small as 0.4 mm. With this level of control, you can print small deposits next to large ones, e.g. 0201s right next to connectors.
Struggling with warped PCB belongs to the past
The paste application during the jet printing process takes place without contact with the printed circuit board, which means that no pressure is applied to the printed circuit board. Complex PCB supports are not necessary. In addition, a height laser in the system measures the height information of the PCB and determines the warpage of the PCB. The system thus determines the topography of the printed circuit board and compensates for it. This way, the solder paste is dispensed at a constant print height above the PCB surface in every printing cycle, regardless of the shape and warpage of the PCB.
Jet printing is also convincing when it comes to sustainability: this technology allows a high degree of control over the paste volume on the pads, which means that the correct amount can be dosed for every single pad. This reduction in solder paste consumption depends on the individual PCB design, but some Mycronic Jet Printer users have reported a double-digit reduction only on the volume of paste needed on the board. On top of this, stencil printing wastes paste through spillages and cleaning etc., which jet printing avoids through the use of solder paste cassettes that simply snap into place.
The future of SMT production is increasingly complex. Denser boards, a wider range of miniaturized components, more NPIs and erratic production schedules. As these high-mix challenges ever increase, real productivity and throughput suffer. And we’ve only just seen the beginning.
At Mycronic, we’ve devoted decades of experience to solving precisely these challenges. With the industry’s fastest, most flexible and most precise jet printing and solder paste dispensing systems.
Mycronic jet printing technology makes it possible to dispense solder paste for the most challenging circuit boards and components, with micrometer accuracy, maximum speed and perfect quality solder joints.
For more information, please visit www.mycronic.com.
