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chchyong89 16th July 2010 10:39 PM

Guide needed. beginner in learning PCB (DIP-TRACE)
Dear everyone, i am new to PCB making, and i am interested in designing a compact SMDs dac for siblings and my girlfriend. I have downloaded a free version diptrace, and my goal is :

-A USB power, i2s out, upsampling, and a WM8741/WM8742.
-Dual layer PCB, no fancy caps, fully smds.

However, i am in the trouble for finding the chips in the diptrace when i started to draw the schematic. Suppose a PCM2707 is using TQFP-32, but i just can't get it find by by entering such keywords under TI.:( Any others keywords to be search?

A simple guide needed to the way of searching for different chips model in DIP-Trace. utmost appreciate with any helping hand.:house:

richie00boy 16th July 2010 11:03 PM

Have you tried looking for the package rather than a specific chip?

chchyong89 16th July 2010 11:06 PM

oh, sorry for the poor england i used:P

i am actually mean how can i search for the package of PCM2707?
There are too many in the TQFP-32 pattern, but none of them are under TI. :(

richie00boy 16th July 2010 11:20 PM

Your English is OK, I understood what you meant. Sorry I can't help. Maybe just try drawing the layout and leave the schematic.

marce 17th July 2010 06:52 AM

2 Attachment(s)
The package mechanical details and the reccomended footprint to IPC-7351 standard. The IPC-7351 standard for PCB footprints covers nearly all PCB required footprints, I'd say that anyone doing SMD PCB design should follow this standard, if for no other reason that th work has been done for you.
My only comment I'd make initialy can you go to a 4 layer PCB, this will be much easier to lay out and more criticaly better for signal integrity.
I would also recomend using a metric grid (0.05mm) and layout. Have a look for a document "The Cad library of the Future" by Tom Hausherr.

Mooly 17th July 2010 07:11 AM

1 Attachment(s)
Have you looked here,

Mooly 17th July 2010 07:15 AM

Also in the free version of Diptrace the 250 pin limit is restrictive. I find if you use individual pads for as many components as you can rather than actual part outlines then you can go over that limit. I use the part initially for pin spacing etc, then match a pad size to it and drag them in place manually if I go over the limit.

chchyong89 17th July 2010 08:03 AM

Thanks mooly for the help,
So the FQFP-32/5X5A has the exactly the pin layout of pcm2707 right?

Do you guys straight away start your drawing using PCB-Layout before using schematic?

marce 17th July 2010 08:33 AM

1 Attachment(s)
Having looked at some of my stuff, a double sided layout would be possible (though not easy), but careful attention will be required to ensure you achieve as near as possible a contiguous ground plane on the bottom of the board.
You have picked some fine pitch devices for a first off PCB design. The Wolfson devices at 0.65mm pitch can be very problematic to solder without solder resist between the pins (shorts). And all the integrated packages are prone to coplanarity problems which can lead to bad joints, so a flat finish (not HASL) will be required for the pads.
Wolson Footprints atached.
I use Cadstar or Allegro, but always the schematic comes first then this is transferred to the PCB directly. Any subsequent changes are done on the scheamtic and ECOed to the PCB. So that the PCB always matches the schematic.

chchyong89 17th July 2010 11:13 AM

Thanks marce, :)

I just finish drawing the layout for the PCM2707 using component editor and attached to FQFP-32/5X5A. "I am kinda worry the footprint matching by the way"

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The last step, where can i search for the spice model for this chip?:rolleyes:

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