good points, and by coincidence we did receive overheated paste yesterday.
While many around the city are still sandbagging, we are also finally
getting some heat. Our paste supplier includes heat sensitive labels and
inspection of the labels at receiving tells if the paste overheated during
transit. We started this additional measure to identify cause of failure
in the past. Once again it was shipped by ground in a slow brown truck,
instead of by air as required( the fault of the courier , not the paste
supplier).
Another frustrating batch of printing defects avoided.
Roger Mack P.Eng.
Manufacturing Specialist
Parker Hannifin Canada
Electronic Controls Division
1305 Clarence Avenue
Winnipeg, MB R3T 1T4 Canada
direct 204 453 3339 x373
[log in to unmask]
www.parker.com/ecd
From:
Mike Fenner <[log in to unmask]>
To:
<[log in to unmask]>
Date:
06-21-2011 06:00
Subject:
Re: [TN] Solder paste Storage and Use
Sent by:
TechNet <[log in to unmask]>
Yes they do. And the information is then continuously verified by feedback
from the field, so that the stated shelf life data given can be relied on.
Interesting thread and much good sense.
I would just suggest a few additional points/clarifications.
Probably most suppliers do not continue to verify paste life until it
"fails". In addition, the shelf life given has to be safe for all users in
all regimes. So some users who do test the paste after the manufacturer's
confirmed life may well find that they can continue to use it. They are
then
in the "engineering margin" as it were.
That would be true for mainstream materials. Specialist pastes are not as
robust in storage, or as tolerant in use as main steam, no clean regular
(SN63/SAC) types. This is down to the alloys simply not being as good at
being solders, so the success/fail bar is lower. In addition, paste in
syringes is likely to have shorter life and be more vulnerable to poor
practice.
The main issue on storage is not keeping the product cold, but being able
to
guarantee that it never gets hot. A constant temperature is better than
variable. Thermal damage is cumulative so any excursion to the warm side
will shorten life and this will add to any previous excursion. There is no
cut off or switching point, but storage above say 30C will accelerate
degradation rapidly: from months to weeks, weeks to days. Then hours. [We
are talking about a heat-activated product after all]. I think the most
succinct description of a controlled environment with no over temperatures
is "refrigerator".
The key way to ensure good paste on the line is to control the rate of
issue.
SOP should include the following elements.
A one-way street, of long-term store, shop store and line. Once issued
from
one stage to the next, there is no return.
Long store is refrigerated; shop/line store is not.
Most SMTa pastes will have a confirmed refrigerated life of six months and
an ambient life of half that. Even a three month refrigerated life would
give about six weeks ambient. Therefore, there is no criticality in
issuing
to the shop store on a weekly basis, and from there to machines daily.
At a practical level
Always use fresh paste to start each work period/shift.
I usually suggest coloured dots be used on jars/cartridges on issuing to
line. (Monday red, Tuesday blue, Wednesday green and so on.) These are
more
visible and therefore easily monitored than written labels. You can write
the week number in the dot.
Regards
Mike
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Karen Tellefsen
Sent: Monday, June 20, 2011 9:23 PM
To: [log in to unmask]
Subject: Re: [TN] Solderpaste Storage and Use
All the big solder paste suppliers do extensive testing to determine
paste
storage life at RT and during refrigeration as well as stencil life.
Stored paste will periodically be tested for viscosity, tack, slump,
printing, reflow etc. That's where shelf lives come from. The storage
time required for the paste to significantly functionally deteriorate is
usually divided by 2 to obtain shelf life. Similar life testing is done
for many products including cleaning products, health and beauty aids,
paint, glue, etc.
You're correct about particle size and flux type. That's why no-clean
paste storage life is typically 6 months with refrigeration and water
clean
paste is typically 3 months.
Karen Tellefsen - Electrical Testing
[log in to unmask]
908-791-3069
Re: [TN] Solderpaste Storage and Use
Robert Kondner
to:
TechNet
06/20/2011 03:26
PM
Sent by:
TechNet <[log in to unmask]>
Please respond to rkondner
Hi,
I do wonder where all these shelf live ideas comes from. Seems to me that
particle size and flux type will make a BIG difference, like a power of
10
or so.
A no clean type 3 paste with low levels of activity would seem (at least
to
me) to last MUCH longer than say type 5 in an active OA flux.
Has anyone ever done reflow studies for different types of old paste? I
don't think a paste manufacturer would do such a test, I expect to get
blasted for even suggesting the idea.
But, Look at this link:
http://www.endtimesreport.com/Prescription_longevity.html
Bob K.
Hmmm, I have a bucket of ancient paste tubes. I should give them a try.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Roger Mack
Sent: Monday, June 20, 2011 3:12 PM
To: [log in to unmask]
Subject: Re: [TN] Solderpaste Storage and Use
Most pastes have a refrigeration spec. which gives it a shelf life of 6
months. If you are using 600g tubes most datasheets will require 8 hours
to
acclimatise. Once out of the fridge we don't return it either, but always
sign initials, date and time on each tube. Create an out of fridge "on
deck"
storage for 3 or 4 tubes, or a daily amount for a line. We use a fixture
that fills from the top and you pull tubes from the bottom like a canned
drink dispenser. If you take one, add a new one to the top from the
fridge.
You will never run into trouble with your acclimitizing time, or pull too
much. Your paste likely has a shelf life for room temperature, so set a
spec. that discards all open tubes when pulled, for say, two weeks or a
month. If you are using jars and storing working paste, sign and date it
as
well and control the out of fridge time for that as well.
Roger Mack P.Eng.
Manufacturing Specialist
Parker Hannifin Canada
Electronic Controls Division
1305 Clarence Avenue
Winnipeg, MB R3T 1T4 Canada
direct 204 453 3339 x373
[log in to unmask]
www.parker.com/ecd
From:
Amol Kane <[log in to unmask]>
To:
<[log in to unmask]>
Date:
06-20-2011 13:27
Subject:
[TN] Solderpaste Storage and Use
Sent by:
TechNet <[log in to unmask]>
I am re-writing our solderpaste use and storage procedures for water
soluble and no clean fluxes (SnPb and Lead-free) to say, in essence the
following:
"To be stored per the manufacturer's recommendations (usually upto 10C),
must be at room temperature before it is dispensed on the stencil (at
least an hour thawing is required). Maximum use period to be 8 hours.
Re-refrigeration and use beyond 8 hours not permitted"
The pushback is to the prohibition of re-refrigeration (for use the next
day) after it is thawed and use beyond 8 hours requirement. These
requirements are due to concerns with moisture absorption by the
solderpaste once thawed (affecting slump) and flux activity (due to
ageing)
What criteria are all the learned folks on technet using for solderpaste
management? Is there any literature available that looks at solderpaste
use limits on time and temperature?
A logical solution would be to do a DOE to look at these parameters, but I
am being asked to come up with something ASAP:). love how these things
work!
Thanks in advance
Amol
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