I echo the thanks. I have thought of asking the warehouse to order
some solder paste so we have it on-hand if we needed it for rework.
Having followed the below discussions I think we will order it as needed
and pay the extra for having it overnighted. I had NO idea there were
such stringent storage/use requirements. Thanks again for a VERY
informative discussion, I've never had to deal with paste before.
EYES-PASTED-WIDE-OPEN
Pat Goodyear
Control Technician
Pacific Gas and Electric
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Amol Kane
Sent: Wednesday, June 22, 2011 8:55 AM
To: [log in to unmask]
Subject: Re: [TN] Solder paste Storage and Use
Guys/Gals, thank you for such a lively discussion on the topic!!....lots
of good information! Dave.....I like the point you make on the SEMCO
tubes and environmental exposure.
So, after condensing all the information in the E-mails, we come away
with these salient points:
1. Re-refrigeration is not recommended
2. refrigerated storage life, unrefrigerated storage life for tubes and
jars, and stencil life are the three parameters that need to be
controlled
Refrigerated Storage Life: Per the manufacturer's
recommendations
Unrefrigerated Storage Life: Upto half the refrigerated storage
life (need to determine based on flux/alloy type,
DOE and manufacturer's recommendations)
Stencil Life: 8 hours max
3. have a long term (refrigerated) storage, a short term "on deck" SMT
storage and point of use 4. have thermal labels on the paste tubes to
sense a over-temperature condition 5. Monitor paste usage at the "on
deck" storage point and point of use to determine quantity and validate
paste performance based on time/temperature conditions
Thanks!!
Amol Kane | Process Engineer
Catalyst Manufacturing Services, Inc.
941 Route 38, Owego NY 13827
Phone: (607) 687-7669 Extn 349 | Website: www.catalystems.com
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Roger Mack
Sent: Tuesday, June 21, 2011 9:48 AM
To: [log in to unmask]
Subject: Re: [TN] Solder paste Storage and Use
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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