Re: gEDA-user: PQFP, LQFP, and TQFP in PCB

[Stephen Meier <smeier@AlchemyResearch.com>]

Dan McMahill wrote:

> Note:  especially with some of the more modern packages, there are often
> times packages which are different mechanically but have the _same_ name
> by different vendors.  Doh!  So, you should check your pin pitch at the
> very least.
>
> -Dan
>  
Very, very, very true!  PCB printout in ps form on a 300 pixel per inch 
laser printout seems reasonably acurate (i haven't tried it on the 1200 
pixel per inch color laser printer yet). If you have a sample part you 
should be able to place it on a printout of the pattern. Then take your 
magnifying glass and see how the device leggs line up with the pads. If 
you have a pattern that your not sure of then let others look at it.

This seems to work with a lot of devices.... until you start using bga 
and flip chips.... then it becomes an ohh god I hope this is correct... 
hey bud... does this look good to you? yea ok then we will risk it....

There is hope... that some of the more automatic pattern generating 
applications will increase the chances that a new pattern will work (if 
you enter the pad locations correctly)....

(for those of you that have used a pattern and built the board then let 
the other users know so they can have more confidence) 
By the way Dan. I am inticipating that the improved resolution will 
decrease my worries on the really small pitch devices ( 8 mils except 
that the solder ball locations are in metric terms) that the pads will 
better fit the devices. I will ask John Griessen to publish (for error 
checking only since i am sure the pattern will have no use to anyone 
other then myself) patterns for my 45 pin 8 mil flip chip at the old 
resolution of 1 mil and the new higher resolution. It will be 
interesting to see how they line up. Did I mention that some of the 
newer devices are going to be 6 mil pitch?

I am also going to make a different kind of pitch. If you are 
comercially using pcb (making money from the boards you are building or 
are reasonably well of and using it for your hobbies) then please note 
that the pcb project on sourceforge has a location for making donations 
to help pay the developers for some of their time. Think of it as an in 
liu of license fee, except for the benefits of; you don't have to pay; 
you get the source code and can make modifications if you need to; the 
project files are not locked up in a proprietary binary form; you get 
free support (here).

Best Wishes,

Steve M.