Eric,

I cannot give you the technical reasons but I can tell you that after
loading "flat padded" parts made of FR4 material that you should probably
find another way. Besides the difficulty/impossibility of inspecting
integrity of the solder joints there is the FR4 material which unless
closely monitored in its assembly loves to warp. Are you making this FR4
material or are you buying it? It will be going through multiple reflows by
the time it has been installed in its final location. How is the coplanarity
after all the reflows? I have had warping of a crystal subassembly with FR4
go 30 mils. What do your customers want?

Dorothy Lush
Manufacturing Engineer

> ----------
> From:         Eric Christison[SMTP:[log in to unmask]]
> Reply To:     TechNet E-Mail Forum.
> Sent:         Thursday, September 13, 2001 8:42 AM
> To:   [log in to unmask]
> Subject:      Re: Conformal Coating
>
> Expert Technetters!
>
> I'd value your opinions on the following.
>
> My company is starting development of a new microelectronics device that
> will be packaged in a new style of package. The substrate of the package
> will be made from FR4 laminate - maybe 0.30mm thick. The package will have
> two concentric rings of pads laid out something like this:
>
>         _______________________________
>         |  *   *   *   *   *   *   *  |
>         |  *                          |
>         |  *    *   *    *    *    *  |
>         |  *    *             *       |
>         |  *    *   *    *    *    *  |
>         |  *                          |
>         |  *   *   *   *   *   *   *  |
>         |_____________________________|
>
> I would have thought the obvious connection style would be BGA but my
> manufacturing minded colleagues want to use plain flat Ni/Au pads.
>
> Is this an acceptable design or are there issues with reliability, PCB
> population etc?
>
> Your opinions would be welcome.
>
> Regards,
>
>
>
> Eric Christison
>
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