Mike,
why do you advice not to mix used paste with fresh one? What someone
can expect to happen, from a reflow and soldering point of view?
(please consider that we are talking about used paste I woudn't think
to have more than 20% in volume to mix on a stencil and also I
wouldn't go for mixing it in only one time, so it gets diluted over a
working shift)
THX, Ivan
Il giorno 11/nov/05, alle ore 12:01, Mike Fenner ha scritto:
> The answer is really you can't tell by testing. Even if you
> duplicated a
> solder paste QA lab on your shop floor, you could test the paste
> and find it
> OK, but still not know how much of its life had been used compared
> to new.
> The best thing to do is to control the rate of issue of paste to
> the shop
> floor and put in place some rules on re-use of paste to make an SOP
> for
> operator. Then for your ISO guy demonstrate you follow the SOP.
> Eg
> Only issue what is used in a shift (commensurate with loading stencil)
> Used paste goes in jars marked used paste. Never mix it with new
> paste.
> Use only new paste to load stencil.
> Old paste is only used to replenish stencil (if you are concerned
> to re-use
> paste)
> Discard used paste after x day
> Also put in some best practice rules: Keep jars closed when not in use
> And so on.
> The precise rate of discard etc can be set arbitrarily or by
> reference to
> your fault rates. [Would give your ISO guy something to do :)
>
> Finally whilst no one condones unnecessary waste, don't forget the
> object is
> to produce products not save paste. Solder costs are a tiny part of
> your
> overall spend, you can't really save a huge amount of money on
> solder, but
> you can easily incur costs with non spec materials. That is the
> real benefit
> of the SOP.
>
> Regards
>
> Mike Fenner
> Indium Corporation
> Pb-free at Productronica
> www.indium.com/productronica/
>
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Yannick Brisson
> Sent: 10 November 2005 19:57
> To: [log in to unmask]
> Subject: [TN] Solder paste control
>
> Hi,
>
> I had a question from our ISO guy asking me how I know that
> the
> paste we use is in good condition? The problem is that he saw our
> operator
> put some old paste back in a empty jar to reuse it the next day. So
> his
> question is how do you know the paste has been on the stencil below
> the
> maximal hour wrote in the datasheet? Do you know any measure than
> I can
> take to certify that the paste in good? like viscosity or something
> else?
> And how I do that? Because I'm pretty sure that is next question
> will be
> how I know the new paste we just receive is good too.
>
> Thank You
>
> Yannick
>
>
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