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Subject:
From:
"Stadem, Richard D." <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Stadem, Richard D.
Date:
Wed, 29 Jul 2009 09:35:34 -0500
Content-Type:
text/plain
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text/plain (357 lines)
I totally understand the tests, Graham, having performed them many
times. You asked for input, here it is.

Using a solder paste evaluation board such as those from IPC, Topline,
Practical Components, or the Heraeus Benchmarker II will provide much
more and much better data than a single 6mm dot of paste agglomerating
into a single ball or, in the case of the wetting spread test, the same
6mm dot of paste spreading out on bare copper on a hot plate.
The Benchmarker board (which I like better than the others) essentially
performs the same type of wetting test on bare copper, except it uses a
series of paste deposits of staggered (increasing) pitch so you can
easily compare the wetting of one paste versus another by counting the
number of deposits that bridge together during reflow. It also provides
the same 6mm dot spread and agglomeration test as performed in the 650
TM. 
Peruse this document to get a good understanding of the tests that can
be performed, and the grading system.
http://www.pori.tut.fi/~jusa/students/ett/TechnicalInfoF640_V10_05.pdf.
This test board was agreed by all of the major paste printers to be the
best one to use in a printing competition amongst themselves.
http://www.ep-teq.com/KohYoung/Comparison%20test%20of%20stencil%20printe
rs%20at%20the%20SMT%202008.pdf.

However, you need to balance the wetting test results against the
results for solder paste slumping, which is also included on the Heraeus
test board. Conversely, if you get a paste that fails slumping, it could
perform better on the wetting spread test simply because it was
impossible to print a good brick. On the other hand, a solder paste that
provides a perfect brick may provide much worse tackiness and will not
retain components placed with a high-speed turret chipshooter. This is
the problem with having all of the individual TM650 test methods; any
solder paste can pass these individual tests to meet minimum
requirements of the industry, and still be a terrible paste to use
compared to others.

The Heraeus Benchmarker II test provides a scoring weight for at least
ten different paste tests, closely aligned with the test methods in IPC
TM650, but better. The Benchmarker test procedure provides test methods
for evaluating wetting spread, agglomeration (anti-spitting), slump at
room temperature, slump at elevated temperature, slump at high-humidity
conditions, tack time, tackiness (very important for high speed
turret-style pick and place machines), open stencil life, voiding, SIR
test, and others I cannot remember.

I have used this method of evaluating solder pastes many times. It is
much better and much faster than performing all of the individual TM650
test methods, uses the actual processes and reflow methods used for
production in the user's facility (when was the last time your company
used a hot plate to reflow SMT parts in production?), and provides a
much better overall scoring system to determine which of the solder
pastes will perform best for your particular application(s). The data
provides information one each solder paste's strengths and weaknesses.

While I much prefer this method for evaluating solder pastes, I
understand that the TM-650 test methods you are working on are designed
to ensure a solder paste will meet at least the minimum requirements to
be classified as acceptable for use in the industry. I would still like
to see a recommended method of paste performance evaluation using the
methods I have described within the TM650 manual. I think both are
needed, tests to verify minimum acceptable performance, and evaluation
procedures using one or more of the test boards I mentioned.

To summarize, attempting to evaluate multiple pastes using the
individual test methods described within TM650 using lab equipment such
as hot plates is very time consuming and does not give good clear
comparison results amongst the paste candidates being tested. Those
standards only provide a means of determining whether a paste meets the
bare minimum performance levels and are not relevant as to how well the
paste will perform in actual production processes.

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Graham Naisbitt
Sent: Wednesday, July 29, 2009 7:49 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
>>
>> GEN3 SYSTEMS LIMITED
>> Incorporating Process Support Products
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>> Southwood Business Park
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>>
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>>
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