soldering small surface mount discretes

[Michael]

Hi - I am working on a board where I am quickly running out of space.
The thing that is killing me the most is all the decoupling caps
around an incredibly sensitive ADC. I need to keep the same number of
caps. Currently I have them all as 0603s, but that's just too big.
This is a prototype that I'll be hand soldering. I've done hundreds of
0603s and I find them as easy as can be. I suspect 0402s won't be that
much of a difference. Now - what about 0201s? Anybody ever tried hand
soldering those buggers? I've also heard that 0201s have a nasty
tendency to tombstone unless you are very careful with your
temperature profiling. Any truth to that?

Thanks!

-Michael

 

[John Larkin]

Hi - I am working on a board where I am quickly running out of space.
The thing that is killing me the most is all the decoupling caps
around an incredibly sensitive ADC. I need to keep the same number of
caps. Currently I have them all as 0603s, but that's just too big.
This is a prototype that I'll be hand soldering. I've done hundreds of
0603s and I find them as easy as can be. I suspect 0402s won't be that
much of a difference. Now - what about 0201s? Anybody ever tried hand
soldering those buggers? I've also heard that 0201s have a nasty
tendency to tombstone unless you are very careful with your
temperature profiling. Any truth to that?

Thanks!

-Michael

How many caps are you using? Which ADC is it?

John

 

[DJ Delorie]

Currently I have them all as 0603s, but that's just too big. This
is a prototype that I'll be hand soldering. I've done hundreds of
0603s and I find them as easy as can be. I suspect 0402s won't be
that much of a difference. Now - what about 0201s? Anybody ever
tried hand soldering those buggers?

Yup. http://www.delorie.com/pcb/smd-challenge/

0201's aren't *that* hard (the 01005's are) but they're not as easy as
0402s. Part of the problem is that the parts are on the order of the
same size as your wire solder and iron tip. Even your pulse is enough
to bump them out of place, so keeping them in place while soldering is
trickier.

What I do now (for 0603s) is manually put down solder paste, place the
parts, and use the iron to reflow the paste while holding the parts
down with tweezers or a toothpick. You don't have to get the iron as
close as with wire solder; you only have to touch the copper trace and
the heat is conducted under the part to melt the paste.

If you can etch a paste stencil, you can put the paste down with that
and use either a hotplate or iron to reflow it. Otherwise, it's still
possible to manually paint the paste if the syringe is small enough.

Note that with the really small parts, both pads heat up at pretty
much the same time even if you only touch the iron to one side. This
means the "solder one pad to hold it down" trick doesn't usually work;
the first pad re-melts when you solder the second pad.

I've also heard that 0201s have a nasty tendency to tombstone unless
you are very careful with your temperature profiling.

With hand ironing, it's not just tombstoning you have to worry about -
it's bumping the parts and messing up the alignment. The surface
tension of the solder on one side can easily move these parts, and
jiggling the solder with the iron moves them too. Even with parts as
big as 0603, I have to hold the parts in place while soldering.

 

[Michael]

Yup. http://www.delorie.com/pcb/smd-challenge/

So you don't have any of those boards left, right? It sounds like a
good idea to make a trial board like that.

0201's aren't *that* hard (the 01005's are) but they're not as easy as
0402s. Part of the problem is that the parts are on the order of the
same size as your wire solder and iron tip. Even your pulse is enough
to bump them out of place, so keeping them in place while soldering is
trickier.

So with 0201s, is there still enough space to hold on to them with
tweezers while soldering them down?

Note that with the really small parts, both pads heat up at pretty
much the same time even if you only touch the iron to one side. This
means the "solder one pad to hold it down" trick doesn't usually work;
the first pad re-melts when you solder the second pad.

Interesting - those buggers sure are teeny. At that size is there any
worry about them getting damaged from the heat? I mean with larger
components there is a whole lot more surface are to dissipate the the
heat.

With hand ironing, it's not just tombstoning you have to worry about -
it's bumping the parts and messing up the alignment. The surface
tension of the solder on one side can easily move these parts, and
jiggling the solder with the iron moves them too. Even with parts as
big as 0603, I have to hold the parts in place while soldering.

I do the same - I always put a dot of solder on one side of the PCB,
pick up the part with tweezers in my left hand, then heat up the dot
again with my iron in my right hand, and place the part at the same
time. Easy as can be.

Thanks,

-Michael

 

[Michael]

How many caps are you using? Which ADC is it?

John

Currently 23 capacitors, 8 of which are fairly large tantalums. The
rest are either 100nf or 1uf, so I think could be pretty easily
replaced with much smaller parts. The ADC is an Analog AD7656.

-Michael

 

[D from BC]

Hi - I am working on a board where I am quickly running out of space.
The thing that is killing me the most is all the decoupling caps
around an incredibly sensitive ADC. I need to keep the same number of
caps. Currently I have them all as 0603s, but that's just too big.
This is a prototype that I'll be hand soldering. I've done hundreds of
0603s and I find them as easy as can be. I suspect 0402s won't be that
much of a difference. Now - what about 0201s? Anybody ever tried hand
soldering those buggers? I've also heard that 0201s have a nasty
tendency to tombstone unless you are very careful with your
temperature profiling. Any truth to that?

Thanks!

-Michael

How come you're not using a hot plate?
D from BC

 

[Michael]

Hi - I am working on a board where I am quickly running out of space.
The thing that is killing me the most is all the decoupling caps
around an incredibly sensitive ADC. I need to keep the same number of
caps. Currently I have them all as 0603s, but that's just too big.
This is a prototype that I'll be hand soldering. I've done hundreds of
0603s and I find them as easy as can be. I suspect 0402s won't be that
much of a difference. Now - what about 0201s? Anybody ever tried hand
soldering those buggers? I've also heard that 0201s have a nasty
tendency to tombstone unless you are very careful with your
temperature profiling. Any truth to that?

Thanks!

-Michael

Along the same lines as my first question: anybody know of any small,
reasonably priced large capacitors? My standard decoupling on a chip
is a .1uf on every Vcc/Vdd and a 10uf cap on each supply line/chip.
I've been using Digi-Key # 478-1751-1-ND, which is a 10uf 10V in a
3216-18 package, costing $.54 in quantities of 100. A bit spendy, but
oh well.

But I want to go smaller. I was just looking through Digi-Key and they
have some 0402 and 0603 tantalums with fairly good looking specs, but
they cost $3 or more each! Ouch. Any options? The M size parts
(1.6x0.85mm) seem like the best alternative, like the 511-1494-1-ND:
6.3V, 10uf, $0.46 in quantities of 100.

Suggestions?

Thanks!

-Michael

 

[Michael]

How come you're not using a hot plate?
D from BC

Actually I'm going to have to use a hot plate to do one of the
components on this board (a BGA).

 

[John Popelish]

Along the same lines as my first question: anybody know of any small,
reasonably priced large capacitors? My standard decoupling on a chip
is a .1uf on every Vcc/Vdd and a 10uf cap on each supply line/chip.
I've been using Digi-Key # 478-1751-1-ND, which is a 10uf 10V in a
3216-18 package, costing $.54 in quantities of 100. A bit spendy, but
oh well.

But I want to go smaller. I was just looking through Digi-Key and they
have some 0402 and 0603 tantalums with fairly good looking specs, but
they cost $3 or more each! Ouch. Any options? The M size parts
(1.6x0.85mm) seem like the best alternative, like the 511-1494-1-ND:
6.3V, 10uf, $0.46 in quantities of 100.

To replace tantalums and small electrolytics, I use a lot of
the 10 uF 10% 25 volt 1206 X5R Panasonic ECJ-3YB1E106K.
These cost $0.55 each in quantity 10 from Digikey and have
about a milliohm of ESR. I've never had to parallel them
with a smaller value, yet.

http://www.panasonic.com/industrial/components/pdf/ABJ0000CE4.pdf

 

[John Larkin]

Currently 23 capacitors, 8 of which are fairly large tantalums. The
rest are either 100nf or 1uf, so I think could be pretty easily
replaced with much smaller parts. The ADC is an Analog AD7656.

-Michael

Those decoupling requirements are insane. I doubt that the chip
actually needs all these caps.

John

 

[John Larkin]

To replace tantalums and small electrolytics, I use a lot of
the 10 uF 10% 25 volt 1206 X5R Panasonic ECJ-3YB1E106K.
These cost $0.55 each in quantity 10 from Digikey and have
about a milliohm of ESR. I've never had to parallel them
with a smaller value, yet.

http://www.panasonic.com/industrial/components/pdf/ABJ0000CE4.pdf

We've sworn off tants for cost and reliability reasons, and off
aluminums because of their low-temperature issues. So we mostly use
ceramics. I think we're using mostly 0.33 uf 0603 for general
bypassing, and for the big stuff we have

0603 2.2 uf 0.09 each

0805 10 uf 0.22 each

1206 22 uf 0.63 ea

or something like that.

John

 

[Michael]

Those decoupling requirements are insane. I doubt that the chip
actually needs all these caps.

John

That's quite possible. Then again, I'm not going to argue with the
guys who designed the part. I need every ounce of accuracy that I can
get out of this thing.

-Michael

 

[Spehro Pefhany]

We've sworn off tants for cost and reliability reasons, and off
aluminums because of their low-temperature issues. So we mostly use
ceramics. I think we're using mostly 0.33 uf 0603 for general
bypassing, and for the big stuff we have

0603 2.2 uf 0.09 each

0805 10 uf 0.22 each

1206 22 uf 0.63 ea

or something like that.

John

Do you know of some good 20uF or so at 75V? They seem to be just above
what's available at Digikey etc. (especially the 75V requirement). I
can put lots in parallel, of course, but it starts to get silly.



Best regards,
Spehro Pefhany

 

[DJ Delorie]

So you don't have any of those boards left, right? It sounds like a
good idea to make a trial board like that.

They're too small to make - practically - in small quantities. I
originally made a batch of 100 kits (so, 100 of each part and shared
FAB costs), and sold them at cost to folks on the gEDA mailing list,
so that we could get some experience with the smaller parts. Each kit
cost $2 plus S&H, but it would have been much more if I had made less.
Even then, I added it to another board I made, to share the FAB costs
across projects.

I put the design files online in case anyone wants to add a dozen or
so to their existing two-layer projects, for their own use. They're
only 0.5" square.

I've thought about doing another run, but I keep mentioning the
project and people keep not asking me to make more ;-)

So with 0201s, is there still enough space to hold on to them with
tweezers while soldering them down?

Not really. The tweezers I have, have needle points. I use one point
to hold the part down (i.e. press down on top, not hold from sides)
while soldering the two ends. Even toothpicks need to be sharpened
with sandpaper to be small enough.

Here's a comparason of 0805, 0603, 0402, 0201, and 01005 parts:
http://www.delorie.com/pcb/0805-01005.html

Close-up of 0201s:
http://www.delorie.com/pcb/0201-parts.html

My first hand-soldered 01005 (right side is 0.4mm pitch IC):
http://www.delorie.com/pcb/first.html

Some microscope pix of various parts on laser printed footprints:
http://www.delorie.com/pcb/smd-challenge/fp-pix/

Interesting - those buggers sure are teeny. At that size is there any
worry about them getting damaged from the heat?

I've found the real problem is mechanical damage. It's really easy to
try to nudge a part into position after soldering one end (i.e. while
melting that end's solder), only to rip the entire cap off that end
because the solder wasn't quite melted enough.

Desoldering pretty much ruins the parts too, assuming you can find
them afterwards.

 

[DJ Delorie]

Actually I'm going to have to use a hot plate to do one of the
components on this board (a BGA).

Take advantage of it, and reflow all the other SMT parts at the same
time.

hotplate experiments:
http://www.delorie.com/pcb/hotplate/

sample hotplate-reflowed boards:
http://www.delorie.com/pcb/m3a/
http://www.delorie.com/house/furnace/pcb2/

 

[Michael]

They're too small to make - practically - in small quantities. I
originally made a batch of 100 kits (so, 100 of each part and shared
FAB costs), and sold them at cost to folks on the gEDA mailing list,
so that we could get some experience with the smaller parts. Each kit
cost $2 plus S&H, but it would have been much more if I had made less.
Even then, I added it to another board I made, to share the FAB costs
across projects.

I put the design files online in case anyone wants to add a dozen or
so to their existing two-layer projects, for their own use. They're
only 0.5" square.

I've thought about doing another run, but I keep mentioning the
project and people keep not asking me to make more ;-)

I have a friend that sells educational electronics kits for hobbyists.
I'm going to try to convince him to make something similar.

If you do another run let me know, I'll take a couple off of your
hands.

Not really. The tweezers I have, have needle points. I use one point
to hold the part down (i.e. press down on top, not hold from sides)
while soldering the two ends. Even toothpicks need to be sharpened
with sandpaper to be small enough.

Ah - that'll be interesting. So with both pads clean and free of
solder, you place the part and hold it down, then solder both sides?
How do you get solder on to it? It seems to me that both of your hands
would be busy. Just put a little on the tip of your iron maybe?

I've found the real problem is mechanical damage. It's really easy to
try to nudge a part into position after soldering one end (i.e. while
melting that end's solder), only to rip the entire cap off that end
because the solder wasn't quite melted enough.

Desoldering pretty much ruins the parts too, assuming you can find
them afterwards.

I pretty much toss all surface mount components that I desolder -
life's too short to try to keep track of them all.

Well - I guess I'll making the big switch from 0603 to 0201 for now.
Hopefully I'll survive. Do the electrical characteristics of the parts
change much from 0603 to 0201?

Thanks,

-Michael

 

[Jeff L]

I have a friend that sells educational electronics kits for hobbyists.
I'm going to try to convince him to make something similar.

If you do another run let me know, I'll take a couple off of your
hands.


Ah - that'll be interesting. So with both pads clean and free of
solder, you place the part and hold it down, then solder both sides?
How do you get solder on to it? It seems to me that both of your hands
would be busy. Just put a little on the tip of your iron maybe?


I pretty much toss all surface mount components that I desolder -
life's too short to try to keep track of them all.

Well - I guess I'll making the big switch from 0603 to 0201 for now.
Hopefully I'll survive. Do the electrical characteristics of the parts
change much from 0603 to 0201?

Caps do - the dielectrics are often very voltage dependant. High k
dielectrics are the worst. Going from a 0603 to a 0402 cap with almost
identical specs can show over a 40% - 60% reduction in capacitance at high
percentages of working voltages. With 0402's, you are usually working at
high percentages of the working voltages.

 

[Jeff L]

Do you know of some good 20uF or so at 75V? They seem to be just above
what's available at Digikey etc. (especially the 75V requirement). I
can put lots in parallel, of course, but it starts to get silly.

There are some that come with a double stacked cap with leads soldered on
the side with high temp solder to hold them together. They were 100v and
around the range in capacitance you were looking for. I can't remember the
brand, but they were larger caps, may be 2010's, I think they were bought at
Digikey.

There is nothing wrong with placing several caps in parallel.

Best regards,
Spehro Pefhany

http://www.speff.com

 

[mpm]

Honestly, I stuggle with 0603's.
I suspect I don't have the right equipment and/or technique.

I just wanted to add (for us Engineers anyway..) that maybe the Eye
Doctors could update their charts. Instead of 20/20 eyesight, we
could have 06/03, or 02/01.?

Just a thought.

-mpm

 

[John Larkin]

That's quite possible. Then again, I'm not going to argue with the
guys who designed the part. I need every ounce of accuracy that I can
get out of this thing.

-Michael

Do you need a very low wideband noise floor? If it's accuracy you
need, oversample and average or lowpass filter. Any real-life sampling
16-bit ADC system will have many LSBs of noise anyhow.

That adc scares me. Some of the nodes are bypasses of active circuits,
and whenever I see strange, unexplained bypassing requirements, I
wonder if the datasheet is hiding ldo-type stability problems, or if
the applications engineer was just being too enthusiastic.

John