Brian,
Your stomach is made by new material better than teflon.... Have you
patent it yet (dupont stock is going to take a hit)?  Is it
reproducable?  (I mean the stomach, not the mixture...)...
 
Jk ;-)
Jack, ok I am stop today...

>-----Original Message-----
>From: TechNet [mailto:[log in to unmask]] On Behalf Of Brian Ellis
>Sent: Wednesday, October 23, 2002 4:01 AM
>To: [log in to unmask]
>Subject: Re: [TN] Cleanliness Testing - When is it clean enough?
>
>
>Doug
>
>I have in my garden: navel, bitter and and ordinary oranges, 
>lemons, 2 types of grapefruit, mandarines, clementines, 2 
>types of grape, 2 types of fig, apricots, peaches and 
>nectarines. Mixed together and allowed to ferment, these 
>produce a Diet Dew substitute which also makes a good flux 
>remover. One has to be careful though; 12 seconds too long in 
>the mixture, it eats away all the solder and copper, as well! 
>At 15 seconds, it also attacks gold and nickel. At 30 seconds, 
>you're left with a pristine sheet of perforated epoxy/glass 
>laminate. Wonderful stuff! :-)
>
>Virgil
>
>Sorry, in my earlier post, I hadn't looked too carefully at 
>what you said and missed out on the batch cleaner. As Doug 
>says, batch cleaners that use the rotary arm (dishwasher) 
>principle often leave much to be desired. This is exacerbated 
>when the same arms are used for wash and rinse, as neither 
>becomes optimised and there is quite a loss of energy just 
>turning the arms. This is why, when I was making batch 
>cleaners, I abandoned rotary arms as long ago as 1978 to use 
>motor driven reciprocating arms, which meant that all the 
>kinetic energy in the fluid was used to clean the boards with 
>solid jets for cleaning and sprays for rinsing, in open 
>circuit. Also, it overcame the problem that Doug
>mentions: assemblies placed in the corners and edges of the 
>baskets were as well cleaned as at the centre. Another problem 
>with single-chamber dishwasher type machines was drying. In 
>the days when we made that type (1975-1978), we found that 
>three-quarters of the hot air we drove through the machine was 
>drying the machine itself, not the boards, with a terrific 
>waste of energy. The result was that the boards that came out 
>were rarely dry: just think what happens. Rinsing is a series 
>of dilutions, but there are always contaminants left in the 
>water, even if your rinse 20 times. When evaporative drying 
>starts, the water starts to
>  withdraw to the sheltered parts from the air movement (i.e., 
>round the components), taking the dissolved contaminants with 
>it. As drying progresses, so the contaminants are laid down 
>round the components, where you least need them. This is why 
>we developed our batch dryer, which used rotary air knives to 
>blast off most of the excess water in the first 20 seconds, 
>taking it and the contaminants up the flue. Only then did we 
>start to evaporate the residual water with hot air evaporative 
>drying. Contaminometer tests demonstrated that the residual 
>ionics were typically only about 20% of what they were with 
>identical assemblies where the drying was totally evaporative. 
>Good drying is part of good cleaning. I can now show you what 
>I mean, as this is now academic, the machines no longer being 
>manufactured, so I have no commercial interest; there is a 7.5 
>minute streaming or downloadable video showing these machines 
>and how they work at http://www.protonique.com/video. I 
>honestly believe that these machines were the fastest, most 
>efficient, most economical (and most capital-cost
>expensive!) batch machines on the market, up to when my 
>company was voluntarily liquidated a couple of years ago. The 
>price precluded sales of vast numbers (I think the total 
>number made was about 65), but many of our customers 
>habitually obtained Contaminometer readings on SM assemblies 
>between 0.1 and 0.3 µg/cm2 eq. NaCl with many cleaning 
>methods. Although the Home Page shows we are no longer an 
>operational company, we still have a lot of data on batch 
>cleaning (technical as well as commercial) at 
>http://www.protonique.com/plcom/files/clean.htm
>and following pages. You can say that this is residual 
>contamination of the Internet :-)
>
>[BTW, the most interesting technical paper is not indexed but 
>linked from the data sheet page - don't ask me why, lost in 
>the mists of time!]
>
>Hope this gives you some extra clues.
>
>Brian
>
>Virgil Lenton wrote:
>> We have recently had some cleanliness testing issues.
>> We are washing SMT CCA's with RMA solderpaste in a batch washer 
>> (AQ400RU) with Armakleen E2001A saponifier. The CCA's are being 
>> cleanliness Tested with an Omega Meter Model 600 SMD without heat.
>>
>> Cards that easily pass cleanliness testing at the 
>14uGNaCl/in squared 
>> acceptance level refered to in MIL-P-28809 have visible traces (under
>> magnification) of whitish flux residue under and around many of the 
>> SMT components.
>>
>> I do understand that the cleanliness tester is not meant to be an 
>> analytical tool, but is a tool to be used for process control.
>>
>> Here are my questions.
>> What do others in the industry do to decide when CCA's are clean 
>> enough? Do you come up with your own acceptable cleanliness 
>test level 
>> using SPC techniques? Any other comments?
>>
>> Many thanks in advance
>> Virgil
>>
>>
>>
>> Virgil Lenton - Manufacturing Engineering
>> SED Systems - A Division of Calian
>> Saskatoon, Saskatchewan
>> Canada
>>
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