Ted,
We only make the bare boards.  But we prefer copper defined pads over SM
defined pads.  There is better ball to pad adhesion.

Happy Holden
Westwood Associates





Ted Kong <[log in to unmask]>
12/15/2003 01:56 PM


        To:     "TechNet E-Mail Forum." <[log in to unmask]>, [log in to unmask]
        cc:
        Subject:        Re: [TN] .5 mm pitch components


Hi Happy,

Thanks for the your feedback.  I noticed that the
no-connect pads can be easily lifted using regular
soldering iron during pad cleaning.  Are you using
some other method of cleaning the pads?  Are you using
solder mask define pads at no-connect pads to avoid
this problem?

Ted

--- Happy Holden <[log in to unmask]> wrote:
> Chris,
> These are really assembly questions and can be
> complex trade-offs.  It all
> depends on who is doing the assembly.  We find a
> large soldermask window
> around each row of pads easiest, but that might not
> match the assembly
> capability.  All types are ordered.  There is also
> an issue of where the
> 0.5mm devices are placed if the panel is large.
> FR-4 moves with any heat
> cycle in assembly and the solder paste may end up
> between the pads.  For
> this reason, customers have us put the solder paste
> on the board, reflow
> it, clean it and then cullender it so the solder is
> flat.  All they have
> to do is flux, place the parts and reflow.
>
> There is no bottom to the pitch that might require
> solder mask.  We do a
> lot of flip chip packages that are 0.2mm pitch with
> SM opening that 0.114
> +/- 0.01mm for SM defined pads.  We have
> experimental boards  now that are
> 0.152mm pitch and require soldermask.
> Its not our job to force an assembler into something
> he doesn't want, but
> rather, to give them the price alternatives of what
> is available and let
> them figure out the SYSTEM COSTS.
>
> Happy Holden
> Westwood Associates
>
>
>
>
>
> Chris Robertson <[log in to unmask]>
> Sent by: TechNet <[log in to unmask]>
> 12/15/2003 11:33 AM
> Please respond to Chris Robertson
>
>
>         To:     [log in to unmask]
>         cc:
>         Subject:        Re: [TN] .5 mm pitch
> components
>
>
> Happy,
> What is your recommendation if someone doesn't want
> to pay the premium
> price
> for a manufacturer that can't hold that?
> Are you an advocate for the all mask or none
> approach? This is the feeling
> that the cost outweighs the fallout from bridging?
> This isn't a trick question. I just know people that
> have a block of
> mask clearance and others that feel that the fallout
> from that is to
> costly.
> Is there a breaking value? I mean is there a pitch
> that you hit that
> almost MUST
> require masking?
>
> Chris Robertson
> [log in to unmask]
>
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