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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