Steve,

Your responce to this question brings a question to my mind.  Why wouldn't I want to use the surface area
of the lead or electrod as that is wetted surface that is supporting the component's weight.  Perhaps the
use of pad surface has been empirically established as a close equivalant, you know one of those Rule of
Thumb deals, it ain't science but it sure works.

Gary Camac

Stephen R. Gregory wrote:

> In a message dated 3/3/99 11:50:49 AM Pacific Standard Time, [log in to unmask]
> writes:
>
> << Can anyone respond with a formula for reflowing a double sided board
>  with active parts on both sides (specifically .0020 TSOP's)?
>  I have seen such a formula with a weight vs. lead area in solder ratio
>  but can not locate. Thanks
>  Patrick Malone >>
>
> Hey Patrick!
>
>     Seems what I remember floating around was 30-grams of surface tension for
> every square inch of pad surface. So then I guess you total up the pad surface
> area available for the part, weigh it, and then go to town...(if the part
> weight to surface area ratio is oakie dokie)
>
>     But instead of going through that drill, I'll just tell ya' I haven't met
> a gull-wing part out there that won't hang upside down for me in
> reflow...'cept maybe some 6 & 8 leaded filters that are out there. I'm sure
> some of you have seen those...ya' know, the ones with the big plastic body,
> pretty tall ones...and anything with a heatsink too. Almost all your passives
> are okay...'cept them rolly-poly MELF's. Most J-leaded parts are okay 'cept
> for ceramic parts and your larger PLCC packages...
>
>      That being said, you gotta have good solderability, a decent reflow
> profile, a smooth running oven conveyer (no jerks or anything like that...and
> no, I'm not talking about people jerks either...although that DOES help things
> if there's none of those around either....hehehe), and a board that doesn't
> wanna bow during reflow. You should be okay..
>
> -Steve Gregory-
>
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