Semantic reproach: it is not the BGA that has scales: 'solder ball
scales' may have been more explicit :-)

Brian

Dave Chapman wrote:
> Scaling - Irregular patterns on the solder joint surface,  particularly of a
> BGA ball, uniform in nature and resembling scales or flakes.
>
>
>                     Causes:
>
>                                 a:  As a solder sphere moves from solid to
> liquid, a volumetric change takes place uniformly across the surface of the
> ball. The solder spheres received enough heat to begin to reflow, but the
> heating process stopped, leaving the solder in its thixotropic or 'pasty'
> phase on the tin/lead phase diagram. This solder did not reach the melt
> point for the proper length of time resulting in lead weeping to the surface
> in the form of lead flakes that are fully connected. Visible scaling can
> indicate that insufficient heat was given to the joint in order to reach
> complete reflow and to allow for enough activation energy to produce a
> proper intermetallic bond. A lack of the intermetallic bond will lead to
> premature joint failure.
>
>
>
>                                 b:  Cooling process too slow after the peak
> reflow temperature was reached. This will lead to intermetallic growth and
> tin/lead separation or a heavy concentration which shows up as a coarse
> grain structure often resembling scales or flakes on the surface of a BGA
> joint.
>
>
> -----Original Message-----
> From: [log in to unmask] [mailto:[log in to unmask]]
> Sent: Wednesday, October 15, 2003 9:48 AM
> To: [log in to unmask]; [log in to unmask]
> Cc: [log in to unmask]
> Subject: Re: [TN] BGA Scaling
>
>
>
> Hi Dave! Can you further define "BGA Scaling"? Its a term I am not familiar
> with.
>
> Dave
>
>
>
>
>                       Dave Chapman
>
>                       <dchapman@CIRCUITS        To:       [log in to unmask]
>
>                       ERVICE.COM>               cc:
>
>                       Sent by: TechNet          Subject:  Re: [TN] BGA
> Scaling
>                       <[log in to unmask]>
>
>
>
>
>
>                       10/14/2003 08:43
>
>                       AM
>
>                       Please respond to
>
>                       "TechNet E-Mail
>
>                       Forum."; Please
>
>                       respond to Dave
>
>                       Chapman
>
>
>
>
>
>
>
>
>
>
>       -----Original Message-----
>       From:  Dave Chapman
>       To: [log in to unmask]
>       Subject: Re: [TN]  BGA Scaling
>
>       I am interested to find information on BGA scaling effect and
>       solution, we saw this phenomena yesterday with a ERSA Scope
>       demonstration. I have searched archives here and at SMTNET but no
>       good information.
>       Dave Chapman
>       Circuit Service
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