Message-ID: <sc512f02.008@jazzfm.com>
Date: Fri, 25 Jan 2002 10:09:34 +0000
From: "Martin Charman" <Martin@jazzfm.com>
To: rsgb_lf_group@blacksheep.org
Subject: Re: LF: RE: SMT Devices
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>Andy:


>There was a techniques described a couple of years ago for using these chips
>dead bug style.  Mount the chip upside down on a piece of unetched PCB.
>Bend the grounding pins down and solder directly to the groundplane.


I've just built a PIC controlled DDS using the AD9832 using a similar technique.  I stuck the chip to a small piece of copper mounted along the middle and between the pins of an 18 pin DIL header and used very thin ecw to extend the legs to the header pins.  I bent the chips' legs very slightly to allow easier access to them with the soldering iron.

Now here are some top tips!

When I got to the 14th leg, the wretched thing fell off so try only to bend the legs once!

I managed to attach a wire to the stub of the leg by cutting a very sharp point onto a length of 22swg tinned copper wire, wrapping the wire around the soldering iron bit, tinning the end as soon as it was hot enough and then prodding the tinned end of a piece of ecw against the stub using the home made soldering bit.  I found it best not to swear too loudly whilst doing this - a steady hand is needed.

I potted the whole (very), ugly construction in epoxy resin and it's worked well ever since!

I used a watchmakers eyeglass (my Dad's an horologist), for the really tricky bits and although it didn't affect me too badly cross-eyed-wise, I suspect Andy's comments should be noted.

Regarding a board for various DDS chips, I have a friend who owns a PCB milling machine which will accept gerber files and will, apparently, cope with SMT devices.  He might be willing to run off a couple of boards if anyone would care to design one?  I haven't asked him by the way so he might not!

73 Martin
G4FKK