[NLRS] LFCSP (was re:power measurement)

[Gerald]

On Fri, 2006-02-10 at 16:59 -0600, Ford Peterson wrote:
> 
> Chris moaned...
> 
> ...snip...
> 
> > And these are indeed very cool...  but how on earth do you work with
> > them at home given the packaging?  The AD8317 (1 MHz to 10 GHz) Log
> > Detector is in a 2mm x 3mm 8-Lead LFCSP package.  Geez!  First you
> > gotta make a board and then you have to figure out how to solder
> > it down.
> > 
> > I just ordered samples of a cool ADI synthesizer (ADF4360-6) that will
> > let me generate 1152 MHz from a 10 KHz GPS reference directly--  and
> > I failed to pay close enough attention to the packaging... and that
> > one too is in a 4mm x 4mm LFCSP package.  I know I am getting old
> > (43) but I never had trouble working with stuff at home until I
> > encountered these beasts.  I had to order the eval board to play.
> > What looked like a $6 project is now $120.  Geesh.
> > 
> > So, how do people make use of these things in a hobby context?
> > 
> > Chris NØJCF
> 
> I feel your pain Chris.
> 
> I found one of the kewelest (turned into a cruelest ...snicker...) RF Gain Block I've ever run into.  The AD8354 is nothing short of awesome.  1 MHz to 2.7GHz fixed 20dB gain block.  Linear output power up to +4dBm.  In/out matched to 50 ohms.  NF 4.2dB.  Vcc 3v or 5v.  Total supply current 23mA.  Compare that power to a MAR!  Input power maximum 10dBm.  This thing looks to be awesome.  Digi-key p/n for either the 8354 (20dB) or the 8353 (25dB) is $1.45.  LFCSP package is new to me.  But the eval board on the data sheet looks like a 1/2 pitch SOIC8 part.  How tough can this be?  So I order up a few just to play...
> 
> What a disappointment!  These are 2mm by 3mm.  8 leads!  4 on each side!  Traces need to be like 0.005"!  The center of each pad is 0.0127" apart!  The eval board graphic in the data sheet must have been blown up by about 4X!  No way does the graphic characterize just how small this stuff really is.  You don't have a good feel for it until you pick one up with the tweezers and see that the needle tweezers shorts out about 3 pins on each side!
> 
> I tried super gluing them upside down to get at the pads on the bottom.  (there are no leads)  Completely hopeless!  My smallest iron touches 3 pads at once!  Short of having a gold wire bonding apparatus, I think this stuff is establishing the limits of homebrewed capability.  I too would be interested to know how these must be placed in production.  
> 
> I feel your pain OM.
> 
> Ford-N0FP
> ford at cmgate.com

They probably are placed by machine over a tiny drop of epoxy to hold
them until they get to the wave soldering machine. Or the traces may
have had a bit of fluxed solder powder (called paste) silk screened
(takes good screens or a machined mask, maybe etched from solid metal)
and then after the epoxy sets the solder was melted with a jet of hot
air. Some have reported for ham projects that applying the solder past
with a syringe and insulin needle then holding the chip down with some
sort of soft adhesive works. One suggestion was from GB of a product not
available here. The other suggestion was to use Staples reusable
adhesive. What I found has part number 10448-US, bar code 7 18108 00907
2. Says it conforms to ASTM D-4236.

A week or so ago I started to attack old surface mount boards in a
Motorola spectra and my tiny iron with a 1/16" diameter tip is still
big. I may have to take a tip and hit it with the lathe to cut it down
to .032. Maybe drill a hole in the end and silver solder in a bit of 20
gauge bus bar and file a flat tip on the bus bar (how ironic that name
which could apply to 1/4 x 4 copper bar or stiff bare copper wire even
the size of hair.

One other possibility might be that an adapter board could be made (or
may exist) to hold the tiny 2 x 4 mm chip and bring out its leads to a
workable perimeter, say 6 x 8 mm. Probably made of FR-4 but .016 thick
so it can be laid on a hot plate, the solder paste melted on the chip
pads and the chip lowered with tweezers.

All these things probably have to be done under a 10 to 20 x stereo
microscope. I have one, but its old and purely vertical so I'll have to
create a special low work bench and there's no room for that around here
right now.

-- 
73, Jerry, K0CQ
Dr. Gerald N. Johnson, electrical engineer
All content copyright, Dr. Gerald N. Johnson