I have been loosely using the 'rule' of 30 grams / sq. inch. (yes,
mixed units)

        It seems to work.

        However, if the pads are too large, the component may swim around on
them.

Joe Hurst

> -----Original Message-----
> From: [log in to unmask] [SMTP:[log in to unmask]]
> Sent: Friday, October 09, 1998 11:42 AM
> To:   [log in to unmask]
> Subject:      [TN] question
>
> problem:  smd components floating off the pads during reflow  (i.e.
> mailbox
> aluminium electrolytic capacitor)(d-packs)
>
> question:  is there any  information (or guidelines) that discuss the
> relationship between component weight and contact surface area with the
> board.
>
> we have mailbox packages that float around during reflow because the
> surface tension of the molten paste is not great enough to prohibit the
> component from moving during reflow.   the problem is also related to
> "smoothness" of the material handling, i.e. no abrupt inertial changes.
>
> we can kinda guess that larger lead/land and pad sizes would keep the
> component in it's appropriate location, but it would be nice to have some
> "rule of thumb ratio" that we can add to our design guidelines.
>
> any help would be appreciated.
>
> M.R. McQueeney
> Advance Technology Engineering
> Chrysler Huntsville Electronics
> (256) 464-2629
> [log in to unmask]
>
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