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Soder Paste Shelf life extension

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#63788

Soder Paste Shelf life extension | 18 February, 2011

The following is my opinion on the Shelf life of the Solder paste. Comments are welcome to support or against it.

Solder Paste users often have the issue of Shelf life expiry condition. Companies including big MNCs, order certain quantities, but due to uncertainty of NPI / NPS and Mass Production schedule dates, some Qty of the paste cross over their shelf life period, which is generally 6 months.

While the Manufacturer recommends not use the solder paste beyond 6 months, still, process engineer and purchase personnel approach the supplier to extend the shelf life.

While the Management and production manager is concerned with controlling the cost of production, by extending the shelf life, I would like to compare this situation similar to other cases. Are we using a date expired milk 2 or 3 days beyond use by Date expiry? Are we willing to use a life saving drug marked with a date of Mfr and Date of expiry after the expiry date and try on a patient? Are we using a stale bread / food items after recommended "use before - date"?

All they undergo ageing procesand we are making up our mind and disposing the items after the expiry date.

When it comes to solder paste many companies want to use it after the shelf life, in order to save cost, and makes attempt with supplier for the shelf life extension and certification, just to convince the quality team which objects for using this.

As the case of Milk, medicines etc the chemicals like flux and additives in the solder paste also undergo ageing and hence the supplier / Mfr cannot guarantee the performance, beyong the shelf life period. Moreover the supplier does not know the conditions of storage, by the user, as recommended in the Product Data sheet.

Hence while it is recommended NOT to use the shelf life paste, in case if the Company wants to use this, for a limited period, it has to be the call by the Quality and Engineering group of the company. The team can run the solder Paste and carefully check all the parameters like Paste Viscosity, printability, flow in the stencil, no hang up, no drying, post reflow printing solder joint appearance, any abnormal solder defects etc, and qualify the same. They can also note the solder paste batch and Lot of PCBs done under this paste for any abnormal reports from field for any functional failure etc.

The production, planning and purchase should improve their coordination for a better inventory rather than running around for such extra activities.

Management should monitor closely such rather taking up this with supplier.

Comments are welcome from all

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#63795

Soder Paste Shelf life extension | 19 February, 2011

Just a thought. What is the real shelf life of the past? Do manufactures low ball the self life to sell more paste. If the past is perfectly good one day before the expiration date is it still bad one day after I doubt it. Right or wrong I have seen companies use expired past and it seems to work well with no clean which seems to last longer. Water soluble past can have more aggressive flux in it which can break down the solder past with time. I am not condoning the use of expired solder past just throwing some thought out there you asked.

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#63797

Soder Paste Shelf life extension | 20 February, 2011

I agreed not to ask the shelf life extension to the maker of solder paste. However, somtimes we have no chioce except using expired or used paste. When I have to, try the first PCB as a test. If Ok, just carry on other boards. Unless, use a new solder paste.

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#63806

Soder Paste Shelf life extension | 23 February, 2011

Does someone with technical knowledge knows what exactly happend with the solder paste after the shelf life pass? What we have seen is sometimes flux separation which disapear after a good mix, and change of viscosity i.e. drying. The tin, silver and active flux components are still there, just the viscosity adjustment component evaporise with the time. We did some experiments with solder paste 2 years old, after adding moisturing agent to the paste to bring back in the original viscosity this paste was used for experiments and it behave same way as normal fresh paste when we did IPC solderability tests. So the vendors are right that they can't guarantee paste characteristics after certain amount of time, but the paste is usable with some adjustments after this shelf life time as well.

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#63808

Soder Paste Shelf life extension | 23 February, 2011

You are very right. There are 2 major factors 1) There is going to be Flux separation. This is basically due to fact that metal particles are heavier than the Flux vehicle system, and due to gravity effect they slowly drift downwards leaving the lighter flux on the top layer. The user can see a layer of flux on the top. 2) Due the normal ageing effect of the flux with time, the activity of the flux can change and degrade in performance.

As the flux is homogeneous mix of Basic, Flux like Rosin / resin flux, activator chemicals/ Thixotropic agent (for pre and post print viscosity control) and dissolving solvents. And as you had pointed out the moisturising agent can be the dissolving solvent . The tricky part of this is the user or vendor cannot find the same constituents to make up the loss , which need to be compatible in their chemistry and function. This makes the recovery nearer to original but not original condition of the paste . Thanks for your input and comments

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#63809

Solder Paste Shelf life extension | 23 February, 2011

(Corrected the Subject line - sorry for Spelling ) You are very right. There are 2 major factors 1) There is going to be Flux separation. This is basically due to fact that metal particles are heavier than the Flux vehicle system, and due to gravity effect they slowly drift downwards leaving the lighter flux on the top layer. The user can see a layer of flux on the top. 2) Due the normal ageing effect of the flux with time, the activity of the flux can change and degrade in performance.

As the flux is homogeneous mix of Basic, Flux like Rosin / resin flux, activator chemicals/ Thixotropic agent (for pre and post print viscosity control) and dissolving solvents. And as you had pointed out the moisturising agent can be the dissolving solvent . The tricky part of this is the user or vendor cannot find the same constituents to make up the loss , which need to be compatible in their chemistry and function. This makes the recovery nearer to original but not original condition of the paste . Thanks for your input and comments

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#63810

| 23 February, 2011

#63811

Soder Paste Shelf life extension | 23 February, 2011

We have a new site that is in the process of starting up and doesn't run much (1 tube every couple weeks). They recently called me about using expired paste. I told them to print a few scrap boards and run them through SPI to verify good print and no sticking to squeegees then run them through reflow (without parts) to verify good wetting and coalescence. Then we did the math and realized that the boards cost more than a tube of paste so it was better just to throw the stuff out.

Be careful that using expired materials doesn't cost more than just buying new.

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#63825

Soder Paste Shelf life extension | 24 February, 2011

PKannan, Your opinion is contrary to J-STD-005 "Requirements for Soldering Paste". Within that document is included specific requirements for re-certification of expired solder paste. Paste that is expired can be used after a simple viscosity test and visual inspection, and its expiration date can be extended for a period of 1/2 of the original shelf life from date of expiration. A form is even included within J-STD-005 that lists the various Test Methods (per IPC TM650, a free download of all accepted Test Methods for a large multitude of things, look it up at http://www.ipc.org)that is used to re-certify the paste. You do not need to go back to the paste vendor or get any other "permission" to extend the life, simply follow the requirements listed in the standard and if it passes, you are good to go. Richard Stadem rstadem@gd-ais.com

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#63827

Solder Paste Shelf life extension | 25 February, 2011

Dstadem,

Thanks for bringing your in valuable experience with the J STD 005 " Requirements of Solder Paste". I fully agree with you that the Solder Paste can be qualified for shelf life by doing simple viscosity test and visual inspection for coalescence test.

Principal manufacturer does these tests and give a certificate of fitness for use for 1 month or more depending on the results, in general. I will look into the extension by 1/2 of shelf period and take up with Principals. Based on this the user customer has to put new shelf life validity on the remaining batch/ Lot of containers.

The practical difficulties are, a) Many user customers, including MNC CEMs are not having the viscometer in their Incoming Quality, in house. Also are not familiar with the JSTD 005, though it is very simple and easy test, to conduct. Their quality dept can do this, but they are more interested in objecting to use this rather than training /equip themselves to re-test and re- qualify the paste . b) So when we request the user to send a sample of this for testing and certification ,to the manufacturers site, this has to be properly refrigerated and packed with ice packing etc to withstand the transit environment and Temperature. There is a risk that they do not pack this well. If there is a drying during the transit it gives faulty results. That is the jars in house may be o.k but the jar sent for testing may give higher viscosity thereby misleading the test and certification operation c) Also if the qty left with for shelf certification is small the cost of sending the sample to Mfr‘s site has to be calculated to finally get numbers which should be beneficial to the company management

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