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February 1999

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Subject:
From:
Edward Brunker <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Thu, 4 Feb 1999 12:12:30 GMT
Content-Type:
text/plain
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     The electronics companies who swear by DOE and Taguchi arrays are
     many. There's the classic example of the Wave solder matrix, two types
     of flux, two pre heat settings, two conveyor speeds and two bath
     temperatures. The wonders of this experimental method are praised
     through out the electronics manufacturing world. Yet nobody ever
     enters the parameter "Pad dimensions". As far as I'm concerned the
     experiment is a pile of rubbish without this. The Array doesn't tell
     us what parameters to enter. Anyway, enough ranting.......

     Don't worry about the semantics regarding the occurence of bridging
     between the new and old oven. Don't consider DOE or Taguchi.
     Convection ovens are the standard, going from IR to Convection is a
     good choice.

     Pad geometry and stencil apertures will have a much more significant
     impact. Establish the dimensions used and we can comment. If their
     geometries aren't suitable then no oven will change the defects due to
     bridging. Not all is being told here. The profile will have an
     influence on bridging, but small compared to the effect of pad
     geometry.
     Establish what flux is being used in the paste.
     Let us know the details and we'll sort you out.


     Regards
     Edward Brunker
     PSION COMPUTERS
     GREENFORD
     LONDON

     ______________________________ Reply Separator
     _________________________________ Subject: [TN] Solder Bridging
     Author:  "TechNet E-Mail Forum." <[log in to unmask]>           Energy
     Technology Systems <[log in to unmask]> at INTERNET
     Date:    03/02/99 10:58


     I have a customer who recently replaced a very old IR reflow oven with
     a brand new convection one. Since the new oven has been installed they
     are noticing an increase in solder bridging on some very fine pitch
     components. Even the customer says that they do not suspect the reflow
     oven but they cannot place a finger on it. Being the manufacturer of
     this oven I want to help prove that it is not the problem as none of
     our other customers have ever complained about solder bridging and
     from my experiences solder bridging has been reduced dramatically when
     switching from IR to Convection. Can anyone suggest additional places
     to look.

     The area I am most suspect of is the conveyor just prior to reflow.
     The reflow has an edge conveyor and the linking conveyor just prior to
     reflow is "power loading" the boards. By power loading I mean the
     upline conveyor is running considerably faster so that the boards
     slide a ways onto the conveyor prior to slowing to match the reflow
     conveyor speed. I have heard that boards can crash into the conveyor
     pins, other boards, etc. when power loaded and cause components to
     shift. Could this be the case?

     I know it can not be related to the energy transfer as the delta on
     their boards was reduced from 40 degrees C to less than 15 (actually 8
     - 15 degrees depending on the board) by switching from IR to
     convection.

     Comments?

     Brian

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