>Date: Tue, 01 Jul 1997 09:46:09 -0400
>To: [log in to unmask]
>From: Denis Meloche <[log in to unmask]>
>Subject: Re: Solder Balls
>
>Look at the MSDS for the wave soldering flux.  If the boiling point for
any component  is above the preheat temperature of the machine it could
well leave liquid present in the through holes.  Convection preheat is much
better at drying out liquid fluxes, however, on a through hole especially
one which has good capillary action there could be a considerable quantity
of liquid in the hole.  Also, the solids could skin over retarding the
evaporation of liquids. In regard to preheat the alcohol bearing fluxes
evaporate at a higher rate than water soluable and take away more of the
preheat.  In contrast the water soluable fluxes are slower to evaporate due
to a typically higher boiling point than alcohol (although alcohols come in
all shapes and sizes).  This may be redundant and fundamental, and I
apologize if it is, but, the actual preheat must be determined by a profile
measurement not just the preheat settings.  At 6 ft/min your speed is
rather high and the total heating cycle must be rather short.  This will
also limit the actual temperature rise of the PWB.  If there are any
components on the board with large mass they will also limit the temp rise
making a profile measurement imperative.  I hope this helps, feel free to
contact me offline.
>Denis Meloche 
>Heraeus Inc
>610-825-6050
>
>At 10:23 AM 6/30/97 -0500, you wrote:
>>     Good morning everyone,
>>     Lately, we are experiencing solder balls on the top side of single 
>>     side PWB.  There are some holes that do not get any components before 
>>     wave solder.  When the board hits wave, it makes "frying" noise and 
>>     next thing you see is solder balls.  There are two bottom pre-heaters 
>>     set at 450 F & 475 F.  Solder temp is 500 F.  Conveyor speed is  6 
>>     fpm.
>>     
>>     This problem occurred in the past and was solved by increasing 
>>     pre-heat temps.  which were originally 325 F & 350 F.  Now we are at 
>>     the peak of  highest component heat ratings.  I checked several boards 
>>     and made sure that there is no flux left on the bottom side before it 
>>     hits solder wave. 
>>     
>>     Any suggestion on what should I try next will help.
>>     
>>     Thanks in advance,
>>     Paresh Patel
>>     Oneac Corp.
>>     (847)816-6000 X-704
>>
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>>

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