Shelf life of solder paste
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From: Tony on 1 Jun 2010 06:31 oparr(a)hotmail.com wrote: >> So if it still performs fine, and cleans fine, there is likely nothing >> wrong with it at all. > > Hence my surprise given a shelf life of only six months. Not certain > whether the brand or the type of solder (leaded, water soluble) is a > major factor. > > On May 31, 10:51 am, Archimedes' Lever > <OneBigLe...(a)InfiniteSeries.Org> wrote: It does depend how it is stored, if the temps are low and it is sealed evaporation will slow. It also depends how critical your process is. If you are pasting 10 panels a minute and using a moving table chip shooter you might find a small reduction in stickyness causes alot of rejects. -- Tony
From: George Jefferson on 1 Jun 2010 09:31 <oparr(a)hotmail.com> wrote in message news:d777b8d0-e710-47d2-8dca-1e2ed2173fbf(a)q8g2000vbm.googlegroups.com... >> Generally depends on the environment and use. The main issue is when the >> thinner dries which happens very slowly. A hotter environment will speed >> up >> the process. > > Originally, I had something called Amtech Syntech (leaded but not > water soluble). Still have the jar....Manufactured date was 1/06 and > expiry date was 1/07. Well, it became useless (hard, no tack)in about > 8 months prompting me to get the Kester in 9/06. > > Didn't expect much better in terms of life expectancy so I'm a bit > surprised that it is not only still useful but performance seems to be > on par with when it was new. Both were refrigerated and handled > similarly. > >> So the real question is "What do you mean by 'work'"? > > Finest pitch I'm using is .8mm, the tack is still there and it > releases from the stencil just fine. Also, I dislodged a 0605 cap > while "hot air popping" a defective chip yesterday. All it took was a > toothpick to bead the cleaned 0605 pads with the paste and replace the > cap. It still works for me. > Right, but they are giving the minimum shelf life for some targeted application. 0.8mm isn't very dense so it might work fine. In any case you have two different companies and so their methods to determine the shelf life will be different. Also two different substances so the chemsitry involed are different. It simply seems that Kester was very conservative. IIRC, the real reason the paste goes "bad" has to do with the stenciling. For fine pitch the paste won't hold the form. There is a technical term for it but I don't remember it. Of course, again, it all depends on what their criteria used was and the specific types of paste. There is some standarization of testing but it depends on a lot of factors. If the Kester works for you then go with them next time ;)
From: Archimedes' Lever on 7 Jun 2010 01:19 On Tue, 01 Jun 2010 11:31:28 +0100, Tony <Nospam(a)nospam.com> wrote: >oparr(a)hotmail.com wrote: >>> So if it still performs fine, and cleans fine, there is likely nothing >>> wrong with it at all. >> >> Hence my surprise given a shelf life of only six months. Not certain >> whether the brand or the type of solder (leaded, water soluble) is a >> major factor. >> >> On May 31, 10:51 am, Archimedes' Lever >> <OneBigLe...(a)InfiniteSeries.Org> wrote: > > >It does depend how it is stored, if the temps are low and it is sealed >evaporation will slow. It also depends how critical your process is. >If you are pasting 10 panels a minute and using a moving table chip >shooter you might find a small reduction in stickyness causes alot of >rejects. Most proper assembly houses utilize a tumbler device to constantly properly 'stir' their paste. It comes out of the fridge, and then goes into the tumbler for a half hour before it goes into the puller.
From: Tony on 7 Jun 2010 10:53 Archimedes' Lever wrote: > On Tue, 01 Jun 2010 11:31:28 +0100, Tony <Nospam(a)nospam.com> wrote: > >> oparr(a)hotmail.com wrote: >>>> So if it still performs fine, and cleans fine, there is likely nothing >>>> wrong with it at all. >>> Hence my surprise given a shelf life of only six months. Not certain >>> whether the brand or the type of solder (leaded, water soluble) is a >>> major factor. >>> >>> On May 31, 10:51 am, Archimedes' Lever >>> <OneBigLe...(a)InfiniteSeries.Org> wrote: >> >> It does depend how it is stored, if the temps are low and it is sealed >> evaporation will slow. It also depends how critical your process is. >> If you are pasting 10 panels a minute and using a moving table chip >> shooter you might find a small reduction in stickyness causes alot of >> rejects. > > Most proper assembly houses utilize a tumbler device to constantly > properly 'stir' their paste. It comes out of the fridge, and then goes > into the tumbler for a half hour before it goes into the puller. Well depends what you mean by 'proper' assembly house. I work with Tier1 CEMs for volume manufacture and have never seen such a thing. Mixing will not prevent drying out, although I guess it is probably used to even out the evaporation in low volume production. In volume production the paste is dispensed onto the print screen and worked in with a squeegy blade or injected through a sealed print head. This mixing occurs on the screen or in the head. Printed paste normally has a life of a hour or so. -- Tony
From: Archimedes' Lever on 7 Jun 2010 11:49
On Mon, 07 Jun 2010 15:53:16 +0100, Tony <Nospam(a)nospam.com> wrote: >Archimedes' Lever wrote: >> On Tue, 01 Jun 2010 11:31:28 +0100, Tony <Nospam(a)nospam.com> wrote: >> >>> oparr(a)hotmail.com wrote: >>>>> So if it still performs fine, and cleans fine, there is likely nothing >>>>> wrong with it at all. >>>> Hence my surprise given a shelf life of only six months. Not certain >>>> whether the brand or the type of solder (leaded, water soluble) is a >>>> major factor. >>>> >>>> On May 31, 10:51 am, Archimedes' Lever >>>> <OneBigLe...(a)InfiniteSeries.Org> wrote: >>> >>> It does depend how it is stored, if the temps are low and it is sealed >>> evaporation will slow. It also depends how critical your process is. >>> If you are pasting 10 panels a minute and using a moving table chip >>> shooter you might find a small reduction in stickyness causes alot of >>> rejects. >> >> Most proper assembly houses utilize a tumbler device to constantly >> properly 'stir' their paste. It comes out of the fridge, and then goes >> into the tumbler for a half hour before it goes into the puller. > >Well depends what you mean by 'proper' assembly house. I work with >Tier1 CEMs for volume manufacture and have never seen such a thing. >Mixing will not prevent drying out, although I guess it is probably used >to even out the evaporation in low volume production. In volume >production the paste is dispensed onto the print screen and worked in >with a squeegy blade or injected through a sealed print head. This >mixing occurs on the screen or in the head. > >Printed paste normally has a life of a hour or so. You are missing the steps. I was talking about handling procedure PRIOR to putting it into the pulling machine. Pulling is a silk screen industry term. That would be the paste stencil machine in terms for you guys that have not been around long. As far as stenciled work goes, if you are leaving it on the board for an hour before it goes into the picker/placer, you have a fucked up process. |