MPM's rheometric pump print head improves stencil printing consistency
MPM's rheometric pump print head improves stencil printing consistency
Keywords MPM, Solder pastes, Stencil printers
MPM has developed the rheometric pump print head (Plate 2), a revolutionary technology that controls precisely the consistency and volume of solder paste applied to a PCB, thereby virtually eliminating the principal source of variation in the solder paste printing process.
The system applies paste directly through the new pump printer head, which exploits a novel (patent pending) air tight circular paste chamber that is continuously fed by a pair of standard paste cartridges.
As it moves across a stencil, a combination of pneumatic pressure applied to the paste cartridges and friction between the paste and stencil causes the paste to continuously roll and mix within the chamber. This allows a precise bead of paste to be pumped directly into the stencil apertures. This is separated cleanly from the main body of paste in the chamber by the tips of a metal shear blade beneath the rheometric pump print head.
Unlike conventional squeegee-based printing, major problems stemming from variations in consistency from the solder paste rolling onto the stencil in open air are completely eliminated because the paste is fully protected within the sealed print head.
Plate 2 MPM's rheometric pump print head
This means low boiling point solvents within the paste flux are no longer allowed to evaporate or cause solder spheres to begin to oxidise while exposed on the stencil. The paste only comes into contact with the stencil at the point of application.
In contrast to existing rectangular designs, the circular symmetry of the chamber further enhances print quality by preventing the formation of paste dead spots or air pockets.
To ensure that precisely the right amount of paste is fed directly into the stencil apertures, MPM's rheometric pump print head exploits a closed-loop pressure feedback system that maintains optimal paste pressure inside the storage chamber. And by using MPM's balanced control print head and tactile sensor technology, the head and board are aligned exactly at all times. This allows the head to float across the stencil and adapt to the changing topography of the board to constantly maintain a consistent seal with the stencil surface.
Paste wastage is also dramatically reduced by between 30-50 percent due to the shearing action of the print head's underside blades, which prevent any excess paste being left on a board during printing. This also removes a lot of hassle for operators because they no longer have to clean the stencil between changeovers.
The print speed is up to twice as fast as traditional squeegee blades. It can also be quickly removed or re-installed during cleaning or after refrigerated storage using MPM's innovative quick disconnect system. When combined with the fact that the need for stencil cleaning is eliminated between changeovers, the result is a significant reduction in cycle times and equally dramatic gain in throughput.
The head can be easily retrofitted to the MPM UP3000 and AP series printers. A very large range of board sizes can be printed through the use of eight different head sizes, each of which can handle a wide variety of stencil sizes.
For further information,please contact: Peter Gibbs, Speedline Technologies, Unit 1, Pincents Kiln Industrial Park, Reading, RG31 7SD, UK. Tel: +44 (0) 118 930 1400; Fax: +44 (0)118 930 1401.
