Checks calendar ...nope not April 1st.
-The fresher the paste the better the solder joint. Agreed
- My dilema here is upper management wants the two lines to share one stencil printer thus saving the cost of purchasing a second printer. They propose to paste ahead, allow second runner to change stencils, paste their pc's, and so on. Is/are management process engineers savvy in the SMT process?? If so then they must know a little bit on failure analysis.
- If shifts end approaches, they offer to store the pasted pc boards in a refridgerator overnight until population the next day. Only if you can guarantee the refridge is plumbed with nitrogen (or inert atmosphere) as most refridges are not oxygen free that contributes to oxidation and they have a high degree of moisture..not good for reflow as can cause a popcorn type situation. Not to mention contamination left behind from yesterdays Chinese food. That General�s Chicken is hell on PCB�s
- Help!! Does anyone out there find this to be a bit odd? Very very Odd
- Where could I find articles or documentation frowning upon pasting ahead? If you are running standards then IPC J-STD-004 may help.
- If I had something written by an "expert" maybe management would leave me alone and simply purchase a second stencil printer. http://www.smtinfocus.com/processguide_printing.html#Environment Quick this site goes away Nov 15th. bummer
And
http://www.loctite.com/int_henkel/loctite/binarydata/pdf/elec_Step_by_Step_Soldering_0801.pdf
A Snippet from Loctite�s Link above: Use of solders with the correct rheological characteristic can eliminate such defects. Environmental variables such as temperature and humidity can affect the rheological characteristics of a solder paste. Solder pastes must be formulated to print satisfactorily across a wide range of environmental conditions, as maintaining a constant environment on the production floor is not always possible. Many electronic manufacturers have multiple locations with varying conditions in their production environment�further on... The ability of a solder paste to print acceptably after a delay in production is critical to reducing defects on the modern production line. A paste�s �abandon time� is defined as the maximum amount of time between two printing cycles that will provide acceptable results without reconditioning or kneading the solder paste or cleaning the stencil. Printer downtime is typically due to placement problems or operator breaks. Solder pastes with long abandon times reduce printer maintenance and solder defects due to paste drying, and improve subsequent processes in the line. Evaluating abandon time is very subjective as the definition of acceptable printing can vary greatly.
Hope this helps and good luck...Mr. Solder paster refridgerator saver guy ... Candiadte for Budweisers Real American Hero Contest http://www.neonowl.net/budlight/
Sorry for the lil joke hopefuly no offense (offence?) is taken...all in good fun.
Seriously looking over the loctite site will help plenty.
Enjoy, Cal
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