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Re: gEDA-user: naming and creation of 54-pin TSOP II (400 mil) footprint, request for help
Hi Jelle,
Jelle de Jong wrote:
> Bert Timmerman wrote:
>> Hi Jelle,
>>
>> On Wed, 2009-05-13 at 14:45 +0200, Jelle de Jong wrote:
>>> Hello everybody,
>>>
>>> I am trying to create a footprint with a correct name using the IPC-7351
>>> Naming Convention for Standard SMT Land Patterns.
>>>
>>> But I am having some issues, i am using the below document to learn about
>>> the naming convention:
>>> https://secure.powercraft.nl/svn/openarm/trunk/working/pcb/documents/footprint-name-spec.pdf
>>>
>>> The footprint I want to make is a 54-pin TSOP II (400 mil), see:
>>> https://secure.powercraft.nl/svn/openarm/trunk/doc/SDRAM/MT48LC16M16A2P-7E/256MSDRAM.pdf
>>> # page 75, 54-Pin Plastic TSOP
>>>
>>> I tried to figure it out but I don't know what the lead span 1(L1) is?
>>>
>>> footprint:
>>> TSSOP-65P-640L1-54N
>>> 54-pin TSOP II (400 mil)
>>> TSSOP pin spacing, lead span 1, pin count
>>> P pin spacing dimension
>>> L1 lead span 1 dimension
>>> N pin count count
>>>
>>> I also learned to create footprints with the following document:
>>> https://secure.powercraft.nl/svn/openarm/trunk/working/pcb/documents/land_patterns_20070818.pdf
>>> I had my ups and downs learning this and had some help trough IRC.
>>>
>>> However the creation of a 54-pin TSOP II seems to be able to automate
>>> using a script.
>>>
>>> I looked at the following, but it uses a license I disagree with and I
>>> can't figure out how it works, I prefer OSI and GPL compatible licenses.
>>> http://www.luciani.org/geda/pcb/pcb-perl-library.html
>>>
>>> Would somebody be able to help me out, what should the name of the
>>> footprint become and what scripts can I use to make the footprint and how
>>> can I do this?
>>>
If you have access to a windoze box you could install the free demo
version of the PCB Matrix Land pattern viewer.
Free as in beer :-(
This is an easy way to get a rough guestimate for land pattern dimensions.
It can be found at:
http://www.pcbmatrix.com/downloads/LPSoftware.asp
BTW: I'm coding a pcb footprint wizard called "fpw" (and a GTK version
called "pcb-gfpw"). Best to google for "pcb-fpw". This is still alpha so
Your Mileage May Vary.
>> I would go for a name like: "TSSOP80P1176X120-54N.fp" as in the IPC
>> standard IPC-7351
>>
>> 0.80 mm pitch,
>> 11.76 mm lead span,
>> X
>> 1.20 mm height
>> - 54 leads with Nominal pad conditions (as one of the following: Least,
>> Nominal, Most).
>>
>> Maybe it is a wise thing to avoid "-" characters in footprint file names
>> or to have a "use-files" line in your gsch2pcb config file and pass a
>> --skip-m4 flag to disable m4 macro generated footprints to goof up your
>> pcb stuff.
>>
>> Maybe include a vendor and part name too, while footprint artwork
>> recommendations may vary across vendors and specific parts.
>>
> Thanks Bert for the feedback, I am confused, I calculated the pitch on
> 0.65 mm how did you came to 0.80mm, and could you explain what exactly
> the lead span is. If I look at page 75 of the datasheet how can I exactly
> calculate this lead span?
>
On page 75 the lead span dimension of the package is given in mm, it's
at the bottom of the top view, it is the maximum width of the package.
This is not to be confused with the toe-to-toe distance of the
landpattern, which will have to protrude from below the leads at least
twice the solder fillet dimension.
The package body itself is 400 mil or 10.16 mm.
> Why did you include the height where did you find this requirement in the
> IPC-7351 for TSSOP footprints?
>
I found a copy over here:
http://www.pcblibraries.com/resources/files/IPC-7351/IPC-7x51%20&%20PCBL%20Land%20Pattern%20Naming%20Convention.pdf
BTW: your Micron SDRAM is in TSOP package, any confusion my mistake ;-)
> And why should one avoid the "-" character in footprint names? I see a
> lot of footprints with this character, would you be willing to discuss
> the arguments?
>
M4 macros may treat this as an operator and try to do some math.
> I call the gsch2pcb with the following arguments:
> gsch2pcb --use-files --skip-m4 ~/openarm/working/gschem/openarm-sbc.prj
> --elements-dir ~/openarm/working/pcb/footprints/
>
Looks good to me, although I recently did my first couple of boards.
Hopes this helps a bit.
Kind regards,
Bert Timmerman.
> I hope that is ok...
>
> Sorry for al the questions, I am kind of confused, and searching for
> answers and help.
>
> Best regards,
>
> Jelle de Jong
>
>
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