On Tuesday 07 August 2012 09:04:25 Peter Homann did opine: > Hi Gene, > > It costs me about $80 for a laser cut stencil. The process of applying > the paste is shown here.
That is I assume 80 AUD. Considering, if that is for a 6mil thick SS stencil, that isn't too bad! > > http://www.homanndesigns.com/index.php?option=com_content&view=article&i > d=54:manual-process-for-applying-solder-paste-via-a-stencil&catid=35:smt > &Itemid=55 That is very similar to what I had in mind, Peter, and it seems to do an excellent job from the pictures. I would add that temporary storage of the pasted board should be in an oxygen-free environment until the board comes out to goto the pick-n-place station, then back into the same low oxygen box while the reflow oven is warming up. > It takes less than 90 seconds to apply paste to a panel with this > method. > > I also have a pneumatic paste dispenser that I use for prototypes and > also for reworking. The paste in the syringes is a lot less viscous so > it can be dispensed through the needle. It is not suitable for use with > a stencil as the stencil paste is not suitable for use in a syringe. Obviously. > I did have a plan to make a paste dispenser machine as I have an auger > driven paste dispenser heat of an old Camalot machine, along with some > nice rails for the X/Y axis. But in the end, the stencil works so well. > If I was doing a lot of one-off, it may be a different story. One day > I'll make it just to see how well it works. > > For an automated dispensing machine an auger dispenser is essential as > the viscosity of the paste changes with temperature. After about 50 > dots from a pneumatic syringe dispenser, the syringe is noticeably > warm, thinning out the paste. When using the pneumatic syringe > dispenser, I'm continuously adjusting the dispense shot time to keep > the dot the size I want. That seems like a needless method then, because it would take far more time to do a board dot by dot than by the stencil method. I wouldn't fix what isn't broken. :) Except of course for one-offs while developing the next design. For that, I'd be tempted to try putting the dispenser head on an XY plotter and stripping the locations to paste out of the eagle (or whatever you use) files so that is largely automated. For that amount of time, the board needs flooded with GN2 which should noticeably improve the quality of the reflowed joint. That reduction in oxides formed is the whole point. Thanks for sharing that Peter. > Cheers, > > Peter [...] Cheers, Gene -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) My web page: <http://coyoteden.dyndns-free.com:85/gene> is up! The profession of book writing makes horse racing seem like a solid, stable business. -- John Steinbeck [Horse racing *is* a stable business ...] ------------------------------------------------------------------------------ Live Security Virtual Conference Exclusive live event will cover all the ways today's security and threat landscape has changed and how IT managers can respond. Discussions will include endpoint security, mobile security and the latest in malware threats. http://www.accelacomm.com/jaw/sfrnl04242012/114/50122263/ _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
