I resisted over three times replying to you question, but let it go
because you were attempting to do the right thing and then you go and
say that.
As long as we are just trying to confirm wetting (without asking your
Mother) and spread ability the 10 second extra allowance for Lead-free
is probably prudent and acceptable. As we attempt to quantify and/or
qualify, there will be a need for more standardization in the process,
as already noted by or esteemed (as previously noted by Mr. Hillman,
this has nothing to do with aging)colleagues. A test vehicle, localized
environmental controls, materials/substrate compatibilities and a
controlled thermal excursion assimilation process will have to be
developed before attempting to establish any metrics for pass/fail
acceptance criteria.
Dewey   

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Graham Naisbitt
Sent: Wednesday, July 29, 2009 5:49 AM
To: [log in to unmask]
Subject: Re: [TN] Solder Paste test method mods

Richard and Inge

These tests which, like all Test Methods, you can download free from  
the IPC web site, are intended to be used by the manufacturers of  
solder paste to give you, the user, a minimum expectation that the  
stuff is any good.

The method in question employs an alumina substrate (specimen) onto  
which the paste sample is printed. The specimen is then placed onto a  
preheated hot plate, reflowed and then examined to check out: wetting,  
spread, solder balling and slump.

As none of them cater for lead-free alloys - yet - we are trying to  
lay down new methods and one of these is, as I mentioned, reflow shall  
occur within 20 seconds of hot plate contact and the proposal is 30  
seconds for lead-free.

Why? Because it has been suggested that the lead-free pastes, because  
of the higher melt temperature, use higher boiling point additives in  
the flux.

So - I am curious to know the views on this both from the paste  
manufacturers stand-point and the end user.

I sometimes marble at Dewey's witisisms.....and then chalk them down  
to experience.

Regards

Graham Naisbitt

Email: [log in to unmask]
Phone: +44 (0)12 5252 1500
Web: www.gen3systems.com

On 28 Jul 2009, at 18:58, Stadem, Richard D. wrote:

> Yes. Some fluxes transfer heat much more readily than others. Not all
> fluxes are designed to burn off prior to reflow taking place,  
> whether as
> a standalone flux or as part of solder paste.
> But I agree that the amount of time is irrelevant; the complete
> agglomeration (no spitting or congealing) of the deposit is what is
> critical in the agglomeration test on ceramic or FR-4, and the  
> degree of
> wetting spread once the paste reaches temperatures above the melting
> point is what is critical on the wetting test on bare copper. The
> variation in test apparatus is too widespread to make the time it  
> takes
> part of a requirement.
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Glidden, Kevin
> Sent: Tuesday, July 28, 2009 12:47 PM
> To: [log in to unmask]
> Subject: Re: [TN] Solder Paste test method mods
>
> Is time to reflow really dependent upon the flux type?  I agree with  
> the
> others - mass, geometry, and of course the alloy metallurgy.
>
> Kevin
>
> -----Original Message-----
> From: Inge [mailto:[log in to unmask]]
> Sent: Tuesday, July 28, 2009 1:29 PM
> To: [log in to unmask]
> Subject: Re: [TN] Solder Paste test method mods
>
> Graham,
>
> I can't see the purpose of such a requirement. Time to reflow is
> dependent
> on the hotplate's surface condition, the contact surface geometry,  
> used
> flux
> and maybe more factors. I  have never seen any useful investigations,
> nor
> any papers on this matter. The time to reflow on a hotplate...what is
> the
> need of that? Heat transfer varies from machine to machine, from  
> process
> to
> process.
>
> Inge
>
> ----- Original Message -----
> From: "Graham Naisbitt" <[log in to unmask]>
> To: <[log in to unmask]>
> Sent: Tuesday, July 28, 2009 5:40 PM
> Subject: [TN] Solder Paste test method mods
>
>
>> Greg and fellow Techies
>>
>> I am in the process of submitting revisions to solder paste tests
> called
>> up in TM-650 and need your help.
>>
>> In 2.4.43 Solder Ball - 2.4.45 Wetting and 2.4.46 Spread Tests, we
> need
>> to allow for lead-free alloys. In each of these there is a quoted
> time:
>>
>> "The reflow shall occur within 20 seconds after the specimen is  
>> placed
> in
>> contact with the hot plate."
>>
>> The recommendation is to include the following:
>>
>> "For lead-free solder pastes, the reflow time shall occur within 30
>> seconds after the specimen is placed in contact with the hot plate."
>>
>> Does anyone out there in Techieland have any objections to this
> proposed
>> addition to each of these test methods?
>>
>> Thanks in advance
>>
>> Regards
>>
>> Graham Naisbitt
>> Managing Director
>>
>> E: [log in to unmask]
>> P: +44 12 5252 1500
>> F: +44 12 5252 1112
>> W: www.gen3systems.com
>>
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