>>> Ryan Grant <[log in to unmask]> 09/19/01 08:26AM >>>
Hi Liu,
Set the object (QFP) on a calibrated flat surface such as a granite block.
You can then use 'feeler gauges' to measure the distance from the block to
the bottom of the lead.
I'm afraid anything other than measuring the perimeter requires more
sophistication, as in the case of measuring the coplanarity of a BGA.
Specialized equipment has been around for decades, but unless you have
access to lots of money and/or make the measurements on a regular basis, its
is impractical to acquire the equipment.
Kind Regards
Ryan Grant
Advanced Technology Engineer
MCMS
(208) 898-1145
[log in to unmask]
> -----Original Message-----
> From: lckang [SMTP:[log in to unmask]]
> Sent: Tuesday, September 18, 2001 6:00 PM
> To: TechNet E-Mail Forum.
> Cc: Ryan Grant
> Subject: Re: Re: [TN] Question about Coplanarity
>
> Hi Grant,
> Thanks for you reply, so if you define it, how to describe? and can
> you suggest some feasible measure methods for it?
>
> Best Regards,
> Liu Changkang
>
>
> *******
> >>>> 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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>
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