Brian and others,

Problems associated with too high a water pressure make perfect sense.  What about cleaning no-lead with water only?  Some equipment advertises higher pressure and higher temperature to counter the effects of the higher reflow temperatures.  Is this a necessity? Does your basic rule of ~2 kW of pump for every meter of wash bar apply for lead free?  Can lead free pcb's be cleaned effectively with water in lower pressure machines of good design or are we being naïve to even think we can effectively clean them with water only?  Too many questions? 

Regards, 
John


-----Original Message-----
From: Brian Ellis [mailto:[log in to unmask]] 
Sent: Wednesday, June 09, 2004 11:41 PM
To: TechNet E-Mail Forum.; John Parsons
Subject: Re: [TN] ASSY: Aqueous Batch Cleaning Equipment

For me, the important things are a) there must be no water puddling 
between the components (i.e., instantaneous draining; if it occurs, it 
will dissipate the kinetic energy of the jets before the water can do 
any work under the components b) the jets should impinge at an acute 
angle to the plane of the board, to ensure there is max ingress under 
the components c) the angle of impingement must vary d) there must be no 
shadowing e) the wash must have solid jets and the rinses very fine 
sprays (water droplet diameter < smallest under-component space) f) the 
pressure is relatively unimportant: it is the energy imparted to the 
water that counts. As a rule of thumb, you need ~2 kW of pump for every 
metre of wash bar. Too high a pressure can even be negative because the 
water tends to bounce off the surfaces. This is the voice of experience 
as an ex-maker of aqueous machines. See my book for more details. g) the 
number of rinses should be sufficient to ensure several replacements of 
water under the tightest component. h) high speed (>200 km/h) air knives 
form an essential part of the cleaning process, also impinging at an 
acute angle, to blast residually contaminated water from under the 
components.

Brian

John Parsons wrote:
> We are looking at adding to our current batch washer (Older Aqueous Tech
> unit) and I am interested in hearing some thoughts as well as first hand
> experience on how the following two cleaning systems work with regards
> to low profile (BGA's etc.) devices run as both conventional and
> lead-free processes.  We are currently running water soluble flux and
> are not using saponifiers for the cleaning process.  I have listed the
> two machines we are considering along with my thoughts.  I am interested
> in hearing yours.
> 
>  
> 
> Aqueous SMT1000
> 
> -         dish washer style loading, poor loading = poor cleaning
> 
> -         vertical loading improves throughput 
> 
> -         high pressure pumps 120psi wash, 45psi rinse for leadfree but
> can this style of machine effectively clean under BGA devices?
> 
>  
> 
> Electrovert Aquajet
> 
> -          large cleaning area (30x30") but horizontal loading would
> appear to limit throughput.
> 
> -          Is any racking available for this machine to process boards
> vertically for increased throughput (within height limitations of front
> opening) or does design technology reduce cleaning cycle when compared
> to Aqueous machine thereby somewhat offsetting loading capacity.
> 
> -          wash and rinse technology coupled with horizontal loading
> seems that it would do a significantly better job on cleaning under low
> profile devices
> 
> Regards, 
> John Parsons
> 
>  
> 
> 
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