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Solder Paste Dispense problems

Rich Z


Solder Paste Dispense problems | 30 November, 2000


I have a reoccurring issue with the Alpha-Metals WS601, water-soluble paste in that the size 20 nozzle of the auger-type dispenser on my Camalot Gemini II clogs up rather frequently. Every few hours we are having to go in and clear out the nozzle. One might just imagine how this affects my through-put. I am hoping someone could point me in the right direction in how I might be able to circumvent this problem. Industry practices???

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Re: Solder Paste Dispense problems | 30 November, 2000

Can't find "WS601" on the Alpha site. What is that stuff?

So, with nothing to go on, I'll just guess ... Yer probably cold welding the solder particles together.

The nozzle size (inside diameter) determines the dot size. * With glue, small dot sizes can be dispensed with a relative small nozzle, for example 0.2mm, but this diameter nozzle does not allow acceptable process times on a substrates with larger components. Normally when dispensing adhesives on substrates with a wide variety of component sizes, a small nozzle is exchanged for a larger one for components, like PLCCs. * With most solder pastes, particle sizes range between 25 microns to 75 microns. Calculate the correct nozzle inner diameter by multiplying 8 times the larger particle size (75 microns above), which equals 600 microns (0.6mm). This is the size nozzle that will dispense solder paste (provided that the paste is still homogeneous) without any cold-welding effect that blocks the nozzle. It�s possible to use the factor of 7, resulting in a 0.52mm nozzle, but this is the absolute lower limit nozzle diameter, assumes homogenous paste, and is a critical value. * With "fine pitch pastes" (e.g., powder of 16-35 microns), select a factor between 10 and 12. This results in a minimum nozzle diameter between 0.35mm and 0.42mm (35�m * factor). Manufacturers intend fine pitch pastes for dispensing on 0.65mm and 1.0mm pitch IC leads. In some cases, they can be used for 0.5mm pitch components, but this substantially slows down the production speed. Fine-pitch solder paste can create lots of little solder balls between IC-solder pads.

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