Dave,
My intention was not to leave you hanging. The reason I said �only you can do the math on that one� is because everybody�s situation is different. Of the 51 � 72% of all solder defects, the portion attributed to a user of 15 mil pitch stencils and BGAs may be different from a user of 25 mil pitch stencils not placing BGAs, or long runs vs. short runs, or a printer equipped with under wipes vs. a printer without, etc. There are too many variables involved for anyone to produce a specific formula that would apply to everyone�s operation. One of the reasons we pay our field representatives the big bucks is to identify those variables so we may recommend specific solutions and justifications.
A good start would be to pull a couple of stencils out of inventory and inspect them under magnification. Since the stencils have been inventoried, I can presume they are as clean as your current process will normally achieve.
Look in the fine-pitch apertures. Do you see any solder paste contamination? Check the surface of the board-side of the stencil for contamination. Check the adhesive bonds for fatigue. Check the tension of the screen. If your current process is using hot wash solution or hot drying air >120 degrees F (49 degrees C.), check the fine-pitch apertures for shape distortion (stainless steel has a very poor memory, once it expands, it doesn�t always contract back to the same position). Check for dings and dents. A good stencil cleaning process should help reduce or eliminate all of these potential problems.
Solder paste will dry in apertures as hard as cement. If a cleaning process did not clean the solder paste when it was fresh, it is unlikely able to clean dry solder paste. The Smart Sonic process will also clean dry solder paste. I have a contract manufacturer customer that inventories hundreds of stencils. He justified the purchase of one of our systems just to remove the dry paste from all of his stencils. Buying new replacement stencils would have cost much more and would have only become contaminated again with his previous cleaning process.
Other issues to consider helping justify a better cleaning process are:
User safety � Are there any health or safety issues associated with your current process? Flammable solvents? Systems using alcohol are known to explode! Many solvents are known to cause birth defects, cancer, etc. If you can smell the solvent � you have a problem.
Cost of operation � Besides the obvious costs such as labor, chemical consumption and energy use to heat it. Does your chemistry require special storage, special transportation? Does your system require ventilation? How much conditioned air is going up the exhaust? What is the cost and effort put forth for waste disposal? Special permits?
To what liabilities is your company exposed? Are you discharging anything to drain? Hauling hazardous waste away? Does your present cleaning process contribute additional waste streams? Are employees exposed to unnecessary health or safety hazards?
I even had a customer justify a process change because his current machine was too complicated.
Please e-mail me directly with your company name, address and phone number and I would be happy to help you evaluate your current process. bill@smartsonic.com
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