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From:
Douglas Pauls <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, [log in to unmask]
Date:
Wed, 22 Jun 2011 08:23:56 -0500
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I miss that Mammoth.  His name was Fred.  It was great riding him into 
work.  Up high with a great view of the area.  Trucks got out of MY way. 
Handled these 20" Iowa snowfalls with ease.  Went through a hell of a lot 
of hay though.  I miss the big guy.

Doug Pauls



"David D. Hillman" <[log in to unmask]> 
Sent by: TechNet <[log in to unmask]>
06/21/2011 07:32 AM
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Subject
Re: [TN] Solderpaste Storage and Use






Hi Richard - good discussion and information! One comment to add - one of 
the advantages of we have with solderpaste shelf/use life today that we 
didn't have back when Doug rode his Mammoth to work is today's modern 
packaging. The SEMCO tubes only expose the solderpaste to surrounding 
environment conditions at its ends - a drastic contrast to opening up a 
jar of solderpaste. And the folks who are using the sealed cartridges also 

have excellent isolation. Not exposing the solder paste to the surrounding 

environment any more than necessary for use has been a key parameter in 
storage/use time.

Dave Hillman
Rockwell Collins
[log in to unmask]




"Stadem, Richard D." <[log in to unmask]> 
Sent by: TechNet <[log in to unmask]>
06/20/2011 04:48 PM
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Subject
Re: [TN] Solderpaste Storage and Use






Please note that solder paste re-certification after shelf life expiration 

IS allowed, and the methods are listed in the solder paste standard 
(J-STD-005), including the test methods from IPC-TM-650 and the forms to 
be used for re-certification.

I have done it several times on many different types of paste and 
different brands, for multiple client companies. I have performed a 
combination of viscosity tests, printing tests including tact time and 
open stencil life, and monitored the DPMO of the product that expired lots 

were used on. The particle size, flux type, leaded or non-leaded alloy did 

not make any difference.

The only thing that mattered (affected the outcome of the test) is the 
amount of flux separation that occurred while the paste was in storage, 
and I only found this to be an issue on ONE major brand of paste (don't 
ask, I won't tell). However, even that paste had zero shift in comparison 
to the controlled samples when properly mixed.

Not surprisingly, expired paste up to 6 months past expiration that had 
been properly refrigerated throughout its entire 12-month storage life 
showed absolutely no difference from paste that had been stored and tested 

exactly the same way BEFORE it expired at 6 months. The six sigma test 
showed a 99% level of confidence there was no difference in defect data. 
(P-value test)

What was really surprising was the overall DPMO. The number of solder 
paste defects as seen during the paste print inspection actually improved 
when expired paste was used! 
Also, the number of solder joint defects seen after reflow also improved! 
This was done using surreptitious testing to avoid any Hawthorne effect 
from the inspectors and operators.

All pastes used are now mixed in an automatic centrifuge made for that 
purpose and the viscosity tested. This eliminates the "sitting at room 
temperature for 8 hours" and assures the viscosity is good from the start. 

The right centrifuge (and the right settings) will provide the exact same 
viscosity and paste temperature every single time a tube is removed from 
the fridge, once you have established what that mix time is.

So, for certain part numbers of solder paste from certain companies, I 
recommended that the shelf life be permanently extended to 1 year, with no 

re-certification requirement after the original 6-month shelf life is 
expired. Remember, this was based on data from repeated testing of several 

lots over time, and the resulting data was carefully reviewed by both the 
client company and its customers. It took a little time to develop that 
database, but it has paid off several times over when smaller EMS 
companies needed to purchase larger lots of paste than they could use 
within the shelf life (most distributors require a minimum buy of 20 tubes 

or so).

A single lot of RMA paste "failed" (displayed much worse test results than 

other candidates during evaluation), but it failed from both the lot 
sample not yet expired, and the lot sample that was 8 months old and 
opened for the first time. The reason why? It was shipped from the 
manufacturer in July, was not kept refrigerated during storage at the 
distributor, and as it turns out, the paste manufacturer re-marked the lot 

expiration date. How do I know? Because when I went to pick it up from the 

distributor, they had ALL of their inventory stored on a shelf at room 
temp, and when I inspected the paste I found the same C of C used on two 
different lots with the same date of manufacture, but different expiration 

dates! Another lot of RMA paste failed because it was shipped frozen in 
dry ice; that is the worst thing you can do to an RMA paste.

So, if you really want to fix your solder paste handling issues, you need 
to control the paste from the manufacturer, certify only distributors you 
can audit periodically, and make sure your purchasing requirements detail 
the proper handling, storage, and shipping methods up to and including the 

dock door (paste should be removed from the insulated container and placed 

into the refrigerator within one or two hours from receipt). You 
absolutely must have some type of internal documentation, training, and 
auditing system to ensure the paste is stored and controlled correctly 
once received.

Please don't use expired paste based on what I just told you. You need to 
ensure you have all of the qualification done to validate YOUR particular 
purchasing, storage, and handling methods for your particular paste. It 
takes very little time, but once done, it pays off over and over. 

Does this all seem like a bit of overkill to you? No problem; never mind 
then, just go back out and support the factory doing all that solder 
touchup.


-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Robert Kondner
Sent: Monday, June 20, 2011 2:26 PM
To: [log in to unmask]
Subject: Re: [TN] Solderpaste Storage and Use

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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