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 ______________________________________________________________________ This email has been scanned by the MessageLabs Email Security System. For more information please contact helpdesk at x2960 or [log in to unmask] ______________________________________________________________________ --------------------------------------------------- Technet Mail List provided as a service by IPC using LISTSERV 16.0 To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL) To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest Search the archives of previous posts at: http://listserv.ipc.org/archives For additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815 ----------------------------------------------------- "PLEASE NOTE: The preceding information may be confidential or privileged. 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