Hello Ryan!
There's a company called Camalot that sells dispensers that in my opinion, make one of the better dispensers on the market. They use what's called a rotary-positive displacement pump when dispensing... much more precise and accurate in my view than other types of dispensers. They've got a pretty good WEB page, and have a column in there called "Dr. Dot" which answers questions about problems people encounter when dispensing. Just click on the link below and it'll take ya' there. I have a freind with a company called ResMed in Austrailia who does nothing but dispense solder paste on his manutacturing floor...he doesn't own a printer or a stencil...does fine pitch too!! Pretty cool if you ask me!
So it is a method of solder paste deposition that I feel hasn't been utilized by most people to it's full extent. Here's some thoughts of a gentleman named Zoran Raich (who works at ResMed) on dispensing...
-Steve Gregory-
The good Points
1: Solder Paste Wastage calculated at 4% (Call me inefficient but we had approx 30% with screen printing in past lives).
2: Safety, operators prefer handling the tubes and is very clean with no mess.
3: Deposition Control. Ever had the problem where you wanted to control the amount paste using stencils but could not or were limited due to fine pitch constraints and aspect ratios (Stepped stencils can be a nightmare). It is interesting to note that coplaniarity issues with finer pitch devices and other IC's are negated dut to the dot height which eliminates dry joints due to coplaniarity issues.
4: Flexibility with regards to frequent design changes, no need to buy multiple stencils through alpha, beta and production stages.
5: No cleaning of stencils or blocked apertures.
6: Paste rheology does not play a large role in dispensing negating the need to constantly work the paste during screen printing to achieve a consistant deposit (Mainly concerned with fine pitch)
7: Change over time between one product and another is as quick as loading another program and changing the Conveyor width (Again no need for stencil maintenance).
The Not so Good Points
1: The solder paste is more expensive for -400 to +500 Mesh (Negated somewhat buy the wastage and waste handling but unfortunately the accountants do not see this, I suspect it has something to do with the personality bypass operation they have after certification)
2: Programming can take a couple of hours to do depending on how many components there are but compared to stencils if you take into account the time taken to do aperture reductions and adjustements creating gerbers emailing them to stencil suppliers liasing with stencil suppliers creating purchase orders la di da etc etc programming time is not as bad as you first imagine.
3: You do sometimes get a missing dot here and there but nothing of major concern a little process control fixes this.
4: It is slower than screen printing, you can not put them in front of fast chip shooters and utilise SMT machines effectively. We are on our boards getting approximately 70% of tact. So please note it depends on your production requirements, we are currently looking at buying the fastest dispenser on the market to take up this issue.
These are some of the more obvious things which may be food for thought and help in the decision making process.
Regards
Zoran Raich ResMed Ltd www.resmed.com.au
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