Homebrew_PCBs

I'm hand soldering 28-pin SSOP's and similar no problem using solder
paste and a heat gun.

Now I've run into an IC I want to use that's in a 16-pin LFCSP !?!

Is this even possible with the same technique or should I just find
another IC? It looks difficult if not damn near impossible.

thanks, Tom

On Tue, 01 Feb 2005 14:20:42 -0000, tkreyche <tkreyche@...> wrote:

>
> I'm hand soldering 28-pin SSOP's and similar no problem using solder
> paste and a heat gun.
> Now I've run into an IC I want to use that's in a 16-pin LFCSP !?!
> Is this even possible with the same technique or should I just find
> another IC? It looks difficult if not damn near impossible.
> thanks, Tom
>

That's one of those nasty ones without proper legs, right?
probably best to use hot air on it.

Dunno why they must torment us with such impossible packages.. What do
they want? Even smaller mobile phones? They need to ship them with
tweezers soon... Oh well, i guess a nice "phone enlarger adaptor"
aftermarktet.

ST

On Tuesday 01 February 2005 09:30 am, Stefan Trethan wrote:

> Dunno why they must torment us with such impossible packages.. What do
> they want? Even smaller mobile phones? They need to ship them with
> tweezers soon... Oh well, i guess a nice "phone enlarger adaptor"
> aftermarktet.

:-)

I remember well reading an article in Popular Electronics, back in the 1960s
some time, where the point was made that with the trend in "miniaturization"
that was started even back then, the ultimate limit wasn't going to be in
the circuitry, but rather in the bits that the operator had to interact
with-- the controls and such.

And while those have gotten smaller than they used to be as well, there is a
limit!

Bigger knobs and switches are easier to operate anyway!

On Tuesday 01 February 2005 09:27, Roy J. Tellason wrote:

> On Tuesday 01 February 2005 09:30 am, Stefan Trethan wrote:
> > Dunno why they must torment us with such impossible packages.. What do
> > they want? Even smaller mobile phones? They need to ship them with
> > tweezers soon... Oh well, i guess a nice "phone enlarger adaptor"
> > aftermarktet.

A number of years ago, I designed a nice little "walky-talky" arrangement for
my wife and I to use when travelling on our motorcycles. Small little
package, clipped onto our helmets, VOX, walkman input, and so on.

Part of this of course required a headphone amp to drive some little speakers
mounted in the helmets.

Went to the National Semi site, did the parametric search and came up with a
suitable candidate. Went to Digikey, there it was, ordered a few.

When the order showed up a few days later, one of the plastic pouches was
empty ! The one with the headphone amp. I was about to get on the phone to
Digikey shipping and whine when something in the bag caught my eye. Closer
examination revealed that it was not a small spec of lint in the bag, but
there was in fact an IC in there.

Back to the NatSemi web site, to the end of the datasheet, stared at the
dimensional info and there realized my mistake. The dimensions I thought to
be in inches (with the decimal point mentally misplaced) were in MILLIMETERS.

I have now added a new criteria to the parts decision. Aside from function,
power, price, availability and so on,

the thing cannot be invisible.

If it's invisible, I have to continue looking. That's my new rule.


Alas, even the days of visible parts are numbered. I went to a seminar on PCB
design done by IBM about 10 years ago. At that time, they passed around a
part that looked a lot like a gull-wing RF transistor. Only the leads were
obviously not any metal I'd ever seen .. they looked almost like mylar,
giving off a weird moire effect when the light struck them just so.

Only under a microscope was it shown that the thing was an IC, with LOTS of
THIN leads coming out each side. The exact numbers escape me, but I think
the leads were .001" wide on .001" centers or something ridiculous like that.

Most of the crowd wanted to know how IBM produced a PCB to support a device
with that fine a pitch; I wanted to meet the poor R&D guy who had to solder
the first one to the prototype.


Alan


--
Alan Rothenbush
Academic Computing Services
Simon Fraser University
Burnaby, B.C., Canada


Before me things create were none, save things
Eternal, and eternal I endure.
All hope abandon ye who enter here.

On Tuesday 01 February 2005 01:02 pm, Alan Rothenbush wrote:

> I have now added a new criteria to the parts decision. Aside from
> function, power, price, availability and so on,
>
> the thing cannot be invisible.
>
> If it's invisible, I have to continue looking. That's my new rule.

Heh. :-)

> Alas, even the days of visible parts are numbered.

I don't know about that. I see people who are embracing surface mount parts
and gearing up to deal with all of that, and I'm just NOT gonna go there! I
have plenty of parts, a pile of boards to scrap yet, and there's lots more
out there, if I can get my hands on it before it hits the landfill. I seem
to be accumulating parts at a much faster rate than I'm using them up, too,
so I'm not real worried about running out any time soon.

Sure, a lot of the industry is headed that way. But ALL of it? I have my
doubts about that. Sure, a lot of parts are getting to where they're only
available in surface-mount packages, but a lot of fairly generic (what I
call "jelly beans") parts are still around, and I tend to design and build
with those anyhow.

> I went to a seminar on PCB design done by IBM about 10 years ago. At that
> time, they passed around a part that looked a lot like a gull-wing RF
> transistor. Only the leads were obviously not any metal I'd ever seen ..
> they looked almost like mylar, giving off a weird moire effect when the
> light struck them just so.
>
> Only under a microscope was it shown that the thing was an IC, with LOTS of
> THIN leads coming out each side. The exact numbers escape me, but I think
> the leads were .001" wide on .001" centers or something ridiculous like
> that.
>
> Most of the crowd wanted to know how IBM produced a PCB to support a device
> with that fine a pitch; I wanted to meet the poor R&D guy who had to solder
> the first one to the prototype.

Anyway!

IBM does do a lot of very weird stuff like that over the years, so it's
really no surprise. Whether such a thing will ever become in any way
"mainstream" I don't know.

I scrapped some boards out years ago, and couldn't figure out what some of
the things on it were. There were resistor packs, pretty obviously, but
those had an assortment of different values in it. I guess it paid them to
make these so that they could save on assembly costs in using ordinary
resistors? Dunno, but they were still through-hole parts. Then there were
these square parts with aluminum cases. Twelve leads or so, if I'm
remembering right. Only IBM part numbers on them, which isn't gonna do me a
whole lot of good (anybody know of a cross-refeerence for those? :-)

So I "took one apart".

Here the major portion of the inside of this thing was filled with what
appeared to be white rubbery material (silicone?), and on top, at each
corner, were these *teeny little* gold wires, going to what appeared to be
a chip, one attached to each corner. Measuring the pins with that in mind
showed these to be transistors!

What possible advantage they could have had to build these parts is beyond me.

On Tue, 1 Feb 2005 12:27:03 -0500, Roy J. Tellason
<rtellason@...> wrote:

>
>
> I remember well reading an article in Popular Electronics, back in the
> 1960s
> some time, where the point was made that with the trend in
> "miniaturization"
> that was started even back then, the ultimate limit wasn't going to be
> in
> the circuitry, but rather in the bits that the operator had to interact
> with-- the controls and such.
> And while those have gotten smaller than they used to be as well, there
> is a
> limit!
> Bigger knobs and switches are easier to operate anyway!
>

Hehe...
A teacher of mine used to say they will soon have to transplant the ear
closer to the mouth, looking at the mobile phones. Well, he was wrong,
they simply used a much bigger airgap between mouth and phone.
I have more than once heared people complain about the size of knobs on
phones, remote controls, etc.....
especially when they get older..


ST

On Tuesday 01 February 2005 02:02 pm, Stefan Trethan wrote:

> On Tue, 1 Feb 2005 12:27:03 -0500, Roy J. Tellason
>
> <rtellason@...> wrote:
> > I remember well reading an article in Popular Electronics, back in the
> > 1960s some time, where the point was made that with the trend in
> > "miniaturization" that was started even back then, the ultimate limit
> > wasn't going to be in the circuitry, but rather in the bits that the
> > operator had to interact with-- the controls and such. And while those
> > have gotten smaller than they used to be as well, there is a limit!
> > Bigger knobs and switches are easier to operate anyway!
>
> Hehe...
> A teacher of mine used to say they will soon have to transplant the ear
> closer to the mouth, looking at the mobile phones. Well, he was wrong,
> they simply used a much bigger airgap between mouth and phone.

We have a cell phone in the family now, and I use it very occasionally, but
I really *hate* the damn thing. It's uncomfortable to hold, and it's way
too easy to hit some button or other that you weren't intending to hit
because it's so darn small and everything is so close together, not to
mention buttons being on the sides where you grip it, etc.

> I have more than once heared people complain about the size of knobs on
> phones, remote controls, etc.....
> especially when they get older..

That's part of it (and I'm pretty sure I'm older than you are by some
nontrivial amount), but it's also fact no matter what the age. I have some
knobs in a box here that are close to 1-1/2" in diameter, with nicely
knurled edges around the outside. Seems to me it would make it very easy to
manipulate a control. Comparing that to these ones that are about 1 cm (!)
or so in diameter, I don't know how they expect people to operate stuff as
reliably, or with as fine a degree of control. Simple physics...

tkreyche wrote:

>
> I'm hand soldering 28-pin SSOP's and similar no problem using solder
> paste and a heat gun.
>
> Now I've run into an IC I want to use that's in a 16-pin LFCSP !?!
>
> Is this even possible with the same technique or should I just find
> another IC? It looks difficult if not damn near impossible.
>
> thanks, Tom
>

Here is an article on the topic of your question;
http://www.edn.com/contents/images/447009.pdf

I assume the package your soldering is 3x3mm LFCSP.
http://www.analog.com/UploadedFiles/Packages/52467337CP16_1.pdf

I've never tried soldering anything that didn't have pins coming out of
the side. Pins with 0.5mm pitch is not impossible with careful control
of all your PCB process methods. I think your only chance is with an
adjustable hot air gun. You may need to modify your hot air gun to allow
a small stream of hot air. Its unfortunate the fan speeds on
conventional hot air guns do not allow flow rate to be adjusted low
enough for SMD rework. These guns have a AC/DC universal motor (like a
hair dryer), so a simple resistor in series with the motor will slow it
down.
The only problem I see is that if you don't have solder mask, then the
self centering action due to surface tension of wet solder may not go as
planned.

On Wed, 02 Feb 2005 10:38:34 +1100, Adam Seychell
<a_seychell@...> wrote:

>
> Here is an article on the topic of your question;
> http://www.edn.com/contents/images/447009.pdf

> The only problem I see is that if you don't have solder mask, then the
> self centering action due to surface tension of wet solder may not go as
> planned.

That article is great, thanks. I think even without soldermask it will
work.
(i have seen some amazing feats of self-centering with unmasked boards.)

I guess one can oven solder the no-leads parts too...

ST

--- In Homebrew_PCBs@yahoogroups.com, "Stefan Trethan"
Adam,

Thanks a million! I second ST's review of the article -- it's one of
the best I've seen....Tom

<stefan_trethan@g...> wrote:

> On Wed, 02 Feb 2005 10:38:34 +1100, Adam Seychell
> <a_seychell@y...> wrote:
>
> >
> > Here is an article on the topic of your question;
> > http://www.edn.com/contents/images/447009.pdf
>
> > The only problem I see is that if you don't have solder mask,

then the

> > self centering action due to surface tension of wet solder may

not go as

> > planned.
>
>
> That article is great, thanks. I think even without soldermask it

will

> work.
> (i have seen some amazing feats of self-centering with unmasked

boards.)

>
> I guess one can oven solder the no-leads parts too...
>
> ST