>>> "Estrada, Roland" <[log in to unmask]> 09/18/01 04:42PM >>>
Good points.
A basic answer to a basic question.
Roland Estrada
Sr. Design Engineer
Electronic Packaging Group
Lockheed Martin - Missiles & Fire Control - Dallas
972-603-0416
-----Original Message-----
From: Jack Crawford [mailto:[log in to unmask]]
Sent: Tuesday, September 18, 2001 3:38 PM
To: [log in to unmask]
Subject: Re: [TN] Question about Coplanarity
>>> Ryan Grant <[log in to unmask]> 09/18/01 01:51PM >>>
Hi Liu,
The definition for coplanarity comes from Geometric Dimensioning and
Tolerancing definitions and exist to prevent confusion. You are mostly
correct in your interpretation, but be careful about re-defining coplanarity
into something more simple because that may cause confusion under different
circumstances.
For example, how do you define the lowest lead? On a four sided QFP, each
four sides will have a single lead that is lower than all the others on that
particular row. However, that lowest lead on one side may never touch the
"established seating plane" and therefore can not be considered the lowest
lead.
Furthermore, suppose one of the rows has all of the leads perfectly in line
with each other, but the entire row is excessively bent. That row would be
the first to contact the "established seating plane" and become the lowest
lead, even though it would appear that row did not have the lowest lead.
From a practical standpoint. We just want to know if all the leads will sit
in solder when placed on a board.
Kind Regards
Ryan Grant
Advanced Technology Engineer
MCMS
(208) 898-1145
[log in to unmask]
> -----Original Message-----
> From: Jack Crawford [SMTP:[log in to unmask]]
> Sent: Tuesday, September 18, 2001 10:41 AM
> To: [log in to unmask]
> Subject: Re: [TN] Question about Coplanarity
>
> >>> lckang <[log in to unmask]> 09/17/01 08:48PM >>>
>
> Hi Technetters!
> According to JESD22-B108 (complanarity test for SMD), the device's
> coplanarity defined as the largest distance distance between the contact
> point of leads and the established seating plane, but when the
> estabilished seating plane is estabilished by three leads which are bend
> downwards, Is it mean that all other device leads are out of planar
> position.
> So can I define it as vertical distance measured from the lowest
> lead?
> Thanks for your any input.
>
> Best Regards,
> Liu Changkang
>
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