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# Chip Mounting

T

#### [email protected]

Jan 1, 1970
0
Hi all,

I'm looking to get back into circuit design. I haven't messed with
anything since my college days - about 15 years ago when I graduated
with an EE. Since then all I've been doing is C/C++ programming work
in embedded systems, but the bug has bit me to do some tinkering
again.

My current project idea has me using some parts I've never done much
with - CPLD's, FLASH, etc. As far as CPLD's, I can get parts I'm
interested in in PLCC packaging, which means I can solder or wirewrap
a PLCC socket. The FLASH I'm looking at is available in TSOP style
packaging.

In general, though - how does a hobbyist go about dealing with these
exotic forms of packaging? TSOP and QFP's are very dense and tiny
surface mounted pins! Are we talking a very chisled point iron,
controlled temps, and a very good magnifying glass? I've seen
adapters that take such packaging out to DIP form, but you still have
to mount the part to the adapter.

What do you all suggest?

D

#### DJ Delorie

Jan 1, 1970
0
In general, though - how does a hobbyist go about dealing with these
exotic forms of packaging?

SMT soldering isn't that hard, even with a standard size iron tip.
Google around a bit, you'll find plenty of tutorials. My way: apply
solder paste to the board (I have a small syringe of it), place part,
heat the paste to solder it, use copper braid to remove any shorts.
It's quick and clean that way.

Once you get used to it, SMD parts are easier to solder than
through-hole parts.
TSOP and QFP's are very dense and tiny surface mounted pins!

I do tssops (0.5mm pitch) and us-8 (0.4mm pitch) chips by hand
(http://www.delorie.com/pcb/smd-challenge/mine-front.jpg), you can
too. 0402s are easy, 0201s are harder, but even 01005's can be done
by hand (http://www.delorie.com/pcb/first.html)
Are we talking a very chisled point iron, controlled temps, and a
very good magnifying glass?

For initial soldering, you're best off with a "hoof" tip, one that can
touch 2-3 pins at once, so you can just swipe it over all the pins. I
use a regular chisel tip for this, though.

Besides that, I use a 0.020" conical (pointy) tip, a temp-controlled
(600F) iron, and a 3.5x magnifying visor.
I've seen adapters that take such packaging out to DIP form, but you
still have to mount the part to the adapter.

It's not hard to make those at home with single-sided copper clad
boards and some FeCl.

R

#### Ron M.

Jan 1, 1970
0
SMT soldering isn't that hard, even with a standard size iron tip.
Google around a bit, you'll find plenty of tutorials. My way: apply
solder paste to the board (I have a small syringe of it), place part,
heat the paste to solder it, use copper braid to remove any shorts.
It's quick and clean that way.

Yep. We have these SMT's where I currently work that we call dust
specks. Takes a 20 power microscope to solder them. Their so small
when you use your tweezers to pick them up you don't have to squeeze.
They are so light just the capacitance of your body will pick em up.

D

#### DJ Delorie

Jan 1, 1970
0
Ron M. said:
Yep. We have these SMT's where I currently work that we call dust
specks. Takes a 20 power microscope to solder them. Their so small

We've named them "quantum capacitors" (the 01005's). One second
they're there, the next second they've vanished. I usually hold my
breath when I'm working with them. I use the 3.5x visor to place
them, then a 60x scope to adjust and/or verify the placement. With
care, though, they can still be soldered by hand.

M

#### [email protected]

Jan 1, 1970
0
You buy an eval board with the CPLD/FPGA or whatever on it first to
try http://www.digilentinc.com/ for some reasonable priced
development boards.

Yep. We have these SMT's where I currently work that we call dust
specks. Takes a 20 power microscope to solder them. Their so small
when you use your tweezers to pick them up you don't have to squeeze.
They are so light just the capacitance of your body will pick em up.

You must not be wearing an approved esd wrist-strap. Isn't that a
firing offense at motorola?

<snip>

D

#### DJ Delorie

Jan 1, 1970
0
You must not be wearing an approved esd wrist-strap. Isn't that a
firing offense at motorola?

More likely, skin oils make your fingers sticky enough (or surface
tension in action) to adhere the parts. The recommended way of
picking up some small parts, for example, is to dip a toothpick in
alcohol to make it just sticky enough to pick and place the parts.

I've found that even the tiniest resdue of flux on my tweezers can
make it very difficult to place the tiny parts, because they don't
weigh enough to stay put when you let go of them - they'd rather stick
to the tweezers.

E

#### Eeyore

Jan 1, 1970
0
Hi all,

I'm looking to get back into circuit design. I haven't messed with
anything since my college days - about 15 years ago when I graduated
with an EE. Since then all I've been doing is C/C++ programming work
in embedded systems, but the bug has bit me to do some tinkering
again.

My current project idea has me using some parts I've never done much
with - CPLD's, FLASH, etc. As far as CPLD's, I can get parts I'm
interested in in PLCC packaging, which means I can solder or wirewrap
a PLCC socket. The FLASH I'm looking at is available in TSOP style
packaging.

In general, though - how does a hobbyist go about dealing with these
exotic forms of packaging? TSOP and QFP's are very dense and tiny
surface mounted pins! Are we talking a very chisled point iron,
controlled temps, and a very good magnifying glass? I've seen
adapters that take such packaging out to DIP form, but you still have
to mount the part to the adapter.

What do you all suggest?

Soldering a TSOP or QFP to an adapter isn't actually as bad as you might think.
You'll need ultra fine solder and an ultra fine tip but it's certainly within
the capability of a competent tech.

Graham

E

#### Eeyore

Jan 1, 1970
0
DJ said:
SMT soldering isn't that hard, even with a standard size iron tip.
Google around a bit, you'll find plenty of tutorials. My way: apply
solder paste to the board (I have a small syringe of it), place part,
heat the paste to solder it, use copper braid to remove any shorts.
It's quick and clean that way.

Don't invest in too much solder paste though. It 'goes off' very quickly. I used
barely a fraction of the syringe I once bought.

Once you get used to it, SMD parts are easier to solder than
through-hole parts.

I do tssops (0.5mm pitch) and us-8 (0.4mm pitch) chips by hand
(http://www.delorie.com/pcb/smd-challenge/mine-front.jpg), you can
too. 0402s are easy, 0201s are harder, but even 01005's can be done
by hand (http://www.delorie.com/pcb/first.html)

For initial soldering, you're best off with a "hoof" tip, one that can
touch 2-3 pins at once, so you can just swipe it over all the pins. I
use a regular chisel tip for this, though.

It's worh adding that it doesn't matter if a few pins are 'shorted together' at
this stage. You can clean up later with solder wick. The wick *with flux* works
best ! I find the 'no-clean' wick utterly useless.

Besides that, I use a 0.020" conical (pointy) tip, a temp-controlled
(600F) iron, and a 3.5x magnifying visor.

It's not hard to make those at home with single-sided copper clad
boards and some FeCl.

I prefer to use HCl and H2O2 to etch actually. FeCl is nasty stuff.

Graham

E

#### Eeyore

Jan 1, 1970
0
DJ said:
We've named them "quantum capacitors" (the 01005's). One second
they're there, the next second they've vanished. I usually hold my
breath when I'm working with them. I use the 3.5x visor to place
them, then a 60x scope to adjust and/or verify the placement. With
care, though, they can still be soldered by hand.

Don't sneeze even with 0603's !

Graham

D

#### DJ Delorie

Jan 1, 1970
0
Eeyore said:
Don't invest in too much solder paste though. It 'goes off' very
quickly. I used barely a fraction of the syringe I once bought.

Mine is SynTECH from stencilsunlimited. The 35g syringe was only $20 complete and it doesn't need to be refrigerated to get a reasonable shelf life. So far I'm happy with it, and if it goes bad, I don't have that much invested in it. http://www.stencilsunlimited.com/solder_products.php It's worh adding that it doesn't matter if a few pins are 'shorted together' at this stage. You can clean up later with solder wick. Yup, I mentioned that. In fact, it's *easier* to solder if you let it bridge the pins occasionally - it takes less time to fix with wick than to avoid the bridges in the first place, and the extra solder ensures a good joint. The wick *with flux* works best ! I find the 'no-clean' wick utterly useless. Wick with flux? I prefer to use HCl and H2O2 to etch actually. FeCl is nasty stuff. Personal preference. I've never had a problem with FeCl, it's cheap and locally available, and only a single chemical is needed. If I stumble upon a local source of HCl and H2O2 I'll try them. B #### Ben Jackson Jan 1, 1970 0 My current project idea has me using some parts I've never done much with - CPLD's, FLASH, etc. As far as CPLD's, I can get parts I'm interested in in PLCC packaging, which means I can solder or wirewrap a PLCC socket. Any modern CPLD is programmable in-circuit, and anything available in PC44 is so simple and cheap that I wouldn't bother socketing it. A PC44 socket that brings the pins out to a PGA is more of a pain to work with than a straight PC package. I just made a CPLD board for a friend as a trial of gEDA, and I wrote it up here: http://www.ad7gd.net/xc9536/ In general, though - how does a hobbyist go about dealing with these exotic forms of packaging? TSOP and QFP's are very dense and tiny surface mounted pins! I've hand-soldered kynar (30ga solid) to adjacent pins on a QFP using a 1/32" tip and no magnification. Of course it helps that I've done similar things under a stereo microscope so I knew what was happening without having to see it. to mount the part to the adapter. Forget adapters. The key is flux. With enough flux, the solder wants to stick to the metal so badly that it's hard to bridge pins. Actually PLCC might be one of the worst SMT packages to deal with, just because the 'hook' part under the chip can bridge and you have to suck that solder out. I'd rather do a TQFP given the choice. R #### Rich Grise Jan 1, 1970 0 . Forget adapters. The key is flux. With enough flux, the solder wants to stick to the metal so badly that it's hard to bridge pins. Actually PLCC might be one of the worst SMT packages to deal with, just because ^^^^ the 'hook' part under the chip can bridge and you have to suck that solder out. I'd rather do a TQFP given the choice. A socket is only$1.85 or so:
http://rocky.digikey.com/WebLib/Amp/Web Photo/New Photos/1-822473-4.jpg

Cheers!
Rich

T

#### TVisitor

Jan 1, 1970
0
Hey all,

Thanks for the comments on the Chip Mounting, it sounds like I have a
lot of options to explore.

FYI, the reason I was talking about adapters to bring it out to DIP
form was so I can stick it in a breadboard and play with my circuit.
Sure, if you had a "real" circuit board, you could do it that way
right away, but I'm not sure how well it lends itself to experimenting
(Unless you had it soldered to a board, and then brought wires off
that board to your circuit...)

After reading all this, a question or two comes to mind:

Let's say I'm not going to use solder paste (which it sounds like most
of you don't go for) but was going to use conventional solder with
flux. If I were going to "slobber" solder all over the pins and then
wick it up, wouldn't I first also have to tin the pads on the board
(otherwise it sounds as if I've got metal pins to metal pads, with
slobber solder all over, but none between the pins and pads!)

Or the other option - conical tip and then carefully soldering each
pin - still, you'd have to tin each pad, correct?

Sorry for the ultra-basic questions, but I guess I've come to the
right group for it

D

#### DJ Delorie

Jan 1, 1970
0
TVisitor said:
FYI, the reason I was talking about adapters to bring it out to DIP
form was so I can stick it in a breadboard and play with my circuit.

Although that was sdip to dip adapter, the theory is similar. I used
female headers as a "breadboard" (22ga wire sticks into them just
fine) and male headers for my logic analyzer.
If I were going to "slobber" solder all over the pins and then wick
it up, wouldn't I first also have to tin the pads on the board

If you've put flux on the pins and pads, the solder wicks between
them. Still, if you're making your own board, it's a good idea to tin
the exposed copper with solder (wiping off the excess with desoldering
braid) to make it more solderable and to avoid corrosion.
Or the other option - conical tip and then carefully soldering each
pin - still, you'd have to tin each pad, correct?

No, but you should flux each pad.

B

#### Ben Jackson

Jan 1, 1970
0
FYI, the reason I was talking about adapters to bring it out to DIP
form was so I can stick it in a breadboard and play with my circuit.

Keep in mind that a PC44 adapter is very wide (will span multiple
breadboards) and not cheap. For the same price (but a bit of a wait)
you could order a pcb from batchpcb with your own design.

I know you are concerned about re-use and flexibility, but if you
want to play with a CPLD, just make one board with some lights and
buttons and play with it.
wick it up, wouldn't I first also have to tin the pads on the board

No. If you're starting with a homemade PCB that's bare copper, it's
easier to solder if you do wet all the pads first. You can do that
with an iron or with tinning solution.

M

#### [email protected]

Jan 1, 1970
0
Hi all,

I'm looking to get back into circuit design. I haven't messed with
anything since my college days - about 15 years ago when I graduated
with an EE. Since then all I've been doing is C/C++ programming work
in embedded systems, but the bug has bit me to do some tinkering
again.

My current project idea has me using some parts I've never done much
with - CPLD's, FLASH, etc. As far as CPLD's, I can get parts I'm
interested in in PLCC packaging, which means I cansolderor wirewrap
a PLCC socket. The FLASH I'm looking at is available in TSOP style
packaging.

In general, though - how does a hobbyist go about dealing with these
exotic forms of packaging? TSOP and QFP's are very dense and tiny
surface mounted pins! Are we talking a very chisled point iron,
controlled temps, and a very good magnifying glass? I've seen
adapters that take such packaging out to DIP form, but you still have
to mount the part to the adapter.

What do you all suggest?

Assuming your pads are pre-tinned, put down a layer of flux. Too
much is better than too little, assuming you can clean the board
later. Tack down the chip, put a tiny bit of solder on the iron (use
flat edged tip, NOT a tiny conical) and wipe across the pin-row semi-
quickly near the bottom. The idea is to not try to solder each
individually, not to depend on the flux in the solder rather than pre-
added flux, and not to try to get a "good" visual looking solder
joint. By this I mean some people see a lot of solder and think
that's good. That's excessive, there should barely be any solder
visible as it's mostly inbetween the lead and pad where it isn't
seen. If there was plenty of flux and the pins weren't horribly
dirty, they will all get coated with solder. If the part was tacked
down flush before soldering you barely need any solder at all, having
too high a solder-added-flux ratio then having to remove excess solder
later is one of the most common mistakes, IMO.

If it doesn't turn out good, put down more flux and reflow with just
the tinned iron tip. Adding more solder is a last resort. A ball of
solder on the iron is too much solder unless the board is pretty rough/
crude/homemade/etc with large gaps. If the gaps are large you might
just take a cold tool and press down the stay pins a little before
soldering. Most people starting out may use 4X as much solder as
needed, roughly. Ideally you get the technique down on scrap chips 'n
boards beforehand.

R

#### Ron M.

Jan 1, 1970
0
You buy an eval board with the CPLD/FPGA or whatever on it first to
try http://www.digilentinc.com/ for some reasonable priced
development boards.

You must not be wearing an approved esd wrist-strap. Isn't that a
firing offense at motorola?

Yep. We wear them faithfully. It doesn't matter with these things.
They are really sensitive to body capacitance. I wish I worked for
Motorola. That would be sweet.

J
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