Maybe OT: Why so much resistance to SMD?

[joegagan]

quote, by doug:
Did you measure all the part values before hand and make sure they matched?


if you are referring to the OD my friend made, i am not sure. he is pretty scientific, but i don't know for sure. also, the well documented effect of the expectation affecting one's perception could certainly come into play. i did not hear these two pedals myself, this was related to me verbally.

as far as my own cap testing , it is admittedly haphazard, but the apparent tone difference has occurred enough over a 10 yr period, i believe i can trust if for my own beliefs.

[Hides-His-Eyes]

why does zvex avoid opamps for signal path wherever possible?

Knowing zvex, it's because then he'd have fewer SHOs in there, and everyone knows the more SHOs the better the pedal

hayyyyoooo

[DougH]

as far as my own cap testing , it is admittedly haphazard, but the apparent tone difference has occurred enough over a 10 yr period, i believe i can trust if for my own beliefs.

I had pretty much sold myself on using high voltage ceramics instead of silver micas in amps. Then just yesterday I subbed a silver mica for a ceramic and much preferred it. In the end I use what I have on my bench that sounds the best. I don't have an LCR meter so I can't really measure them accurately to check for differences in values due to tolerance. I don't know what the reason is for the sonic differences I hear. So I don't make generalizations anymore about "this type vs. that type". I just use what I have on hand that sounds best.

[defaced]

I had pretty much sold myself on using high voltage ceramics instead of silver micas in amps.

There was a really good discussion over at Music Electronics Forums that hashed out the ceramic cap thing.  Basically breaking down the different grades of ceramic caps (I didn't know there were grades of ceramic caps until I read this) and how some are better for amps than others.  May be worth the read.  Now that I'm stocking up on parts, I need to go back and re-read it. 

[markeebee]

Just a thought.....if you put a big splosh of solder paste on the pad/lead junction of a through hole board, couldn't you then flow the paste in an oven a la SMD?  Isn't that the best of both worlds, given that the uber-miniaturisation of SMD doesn't seem to be a big plus point for everybody?

[GBlekas]

I have worked on both through-hole and SMD and one disadvantage of SMD for small components that has not been mentioned is the lack of strain relief.  If you flex a through-hole board, nothing happens because the leads bend.  If you flex an SMD board, devices lose contact or fall off.  Leadless components (passives and leadless IC's) do not work very well over the temperature range you would expect to see as a touring musician.  As a studio queen, they may be OK.  Gullwing devices are generally OK.  Over the temperature range, the temperature coefficient of the circuit board is much larger than the ceramic components.  The most important thing to design for is abuse and they do not tolerate much of it.  Quite often you get intermittent connections that work some of the time but are simply pushed together with a fractured solder connection.  Through hole may have this problem, but it would be the quality of the solder joint, not the fundamental design that is at fault.

Excellent points!  These exact points were told to me by a designer that uses smd with advanced degrees in engineering he stated simply don't put parts near the jacks (input/output/power) which is where a huge manufacturer makes their mistakes.

The best pro point for smd, that I can see is you can fit a lot of stuff in a small package.
That being said I suggest making the same exact pedal with smd, 1/8 watt through hole, 1/4 watt through hole and 1/2 watt through hole and tell me if you hear the difference.
I did this  with an over drive pedal and the difference made smd a "no sale" to me.
Smd would probably be better suited to  applications other than OD  so perhaps modulation based effects or tuners  smd would be fine.

Funny how it all seems to be about the ease  of build, size or cost.....what about the tone ?
IPods are cool but I dont want my rig to sound like one but I play out and dont just build  these things...got to use them in the real world.
It comes down to the impression it leaves on others in the live application, imho.

[DougH]

I've always been taught that solder is not a mechanical connection in and of itself. It is intended purely as an electrical connection. So I wonder how SMD gets away with "breaking the rules".

[markeebee]

Just a thought.....if you put a big splosh of solder paste on the pad/lead junction of a through hole board, couldn't you then flow the paste in an oven a la SMD?  Isn't that the best of both worlds, given that the uber-miniaturisation of SMD doesn't seem to be a big plus point for everybody?

Ah yes.  That's reflow soldering.  I should have known that.

[joegagan]

why do we gotta get all hung up on the rules , man? can't we all just do our own thing and hang out in the park like the old days?

[Gurner]

why do we gotta get all hung up on the rules , man? can't we all just do our own thing and hang out in the park like the old days?

The parks are much smaller nowadays, so SMD techniques are essential if you want a decent go on the swings.

[amptramp]

I've always been taught that solder is not a mechanical connection in and of itself. It is intended purely as an electrical connection. So I wonder how SMD gets away with "breaking the rules".

You should see what happens when you put parts on both sides of the board - you attach one side by vapour phase soldering then flip the board over and the surface tension of the solder is supposed to hold the parts on the board even when they are facing down as you solder parts on the other side.  Basically, the parts are so light that there is very little strength needed.

[Gurner]

I've always been taught that solder is not a mechanical connection in and of itself. It is intended purely as an electrical connection. So I wonder how SMD gets away with "breaking the rules".

You should see what happens when you put parts on both sides of the board - you attach one side by vapour phase soldering then flip the board over and the surface tension of the solder is supposed to hold the parts on the board even when they are facing down as you solder parts on the other side.  Basically, the parts are so light that there is very little strength needed.

Having never ventured into double sided SMD, I could be wrong here - but isn't that when they use glue (cream) on SMD components .....ie for flipping the board over & not having the components fall off?

[frank_p]

I've always been taught that solder is not a mechanical connection in and of itself. It is intended purely as an electrical connection. So I wonder how SMD gets away with "breaking the rules".

I don't understand what you mean Doug...
there is diffusion (ion migration) going on at junction.
http://www.aws.org/wj/supplement/sangha/sangha.html

[R.G.]

N.B. Some SMD work is/swas done by holding the component in place with a dot of epoxy before soldering. When this is/was done, later soldering didn't move the part.

[G. Hoffman]

Personally, I use through-hole stuff because I find it easier to work with.  BUT, if I need to make something small, or to use something which is only available in SMD, then I'll use SMD. 

For those interested in doing SMD, though, I just stumbled across THIS, which you might find interesting/useful. 


Gabriel

[defaced]

I've always been taught that solder is not a mechanical connection in and of itself. It is intended purely as an electrical connection. So I wonder how SMD gets away with "breaking the rules".

I don't understand what you mean Doug...
there is diffusion (ion migration) going on at junction.
http://www.aws.org/wj/supplement/sangha/sangha.html

Is that the right link?  That paper talks about diffusion brazing of copper/tin joints in a nuclear environment at temperatures/pressures that are not at all representative of electronics soldering. 

[frank_p]

I've always been taught that solder is not a mechanical connection in and of itself. It is intended purely as an electrical connection. So I wonder how SMD gets away with "breaking the rules".

I don't understand what you mean Doug...
there is diffusion (ion migration) going on at junction.
http://www.aws.org/wj/supplement/sangha/sangha.html

Is that the right link?  That paper talks about diffusion brazing of copper/tin joints in a nuclear environment at temperatures/pressures that are not at all representative of electronics soldering.  

I was searching broadly microscope shots where we could see a diffusion layer.  This might not be the same temperature and context of use but I tought that in * general brazing process* there is this layer and it provides a good mechanical bonding.  Not just good electrical contact. Here are *macroscopic* views in a more appropriate context tthat show where cracking happens. I have *a belief* that brazing is a pretty good mechanical joint even at the *electronic soldering* temperatures.

http://www.espec.co.jp/english/tech-info/field_report/2-1/detail2-1.html

Cu3Sn is the closest phase layer there is near the Cu layer, then Cu6Sn5.  Those intermetallic phases start at 200 deg. C. on the phase diagram I have just under my nose. Go up at 350 and you can have 5 different phases coexisting with each other.
http://www.metallurgy.nist.gov/phase/solder/cusn.html
The diagram shows that copper is soluble in tin at low temperatures.
CuPb phase diagram:
http://www.metallurgy.nist.gov/phase/solder/cupb.html
For your soldering wire:
http://www.metallurgy.nist.gov/phase/solder/pbsn.html
So this intermetallic layer DO exist at *our 350 deg.* temperature (and by extent are part of the mechanical structure of the bond).  I doubt that the pad could even be wettable if one of those phases could not occur, but of course I may be wrong.

[Gordo]

turn it on....after about 90 seconds, marvel at all the components self aligning themselves as the solder paste flows.

Remove, & be amazed at how everything aligned so well.

Hmmm, you've got my interest now...

[defaced]

I was searching broadly microscope shots where we could see a diffusion layer.  This might not be the same temperature and context of use but I tought that in * general brazing process* there is this layer and it provides a good mechanical bonding.  Not just good electrical contact. Here are *macroscopic* views in a more appropriate context tthat show where cracking happens. I have *a belief* that brazing is a pretty good mechanical joint even at the *electronic soldering* temperatures.

I'll gather that Doug's comment is that you shouldn't rely on the mechanical properties of the joint for support of the component.  Yes, brazed and soldered joint have mechanical properties.  There are even test in welding code documents on how to test these joints for procedure and operator qualification.  I bet you can find ASTM codes that outline it too.  Typical brazed structural joints have strengths in the vecinity of 90ksi.  That's 90,000 psi.  That's more than most structural welds performed, which are around 70 ksi. 

Assuming you're working with eutectic solder, which melts/solidifies at ~175c, the Cu-Sn phase diagram at that temp shows four possible phases.  However, the copper never melts.  Phase diagrams shows what happens when you take an alloy from melting and cool it under equilibrium conditions to whatever temperature indicated.  It says nothing about when you take a solid (Cu) and a liquid (Pb&Sn) and warm it up.  Thus, no intermetallic phase can be formed during our soldering operations (which isn't necessary the only source of mechanical strength). 

The diffusion part of the process mentioned in that paper is caused by time, temperature, pressure, and alloys.  If you remove one of those, namely time and pressure in our case, diffusion does not take place. 

The solder cracking paper is discussing what happens in the solder joint itself, and the addition of elements to the solder which form intermetallics within the joint - not forintermetallics between the joint and the base metal - to prevent cracking.  It's a grain size issue, same thing happens in welds, particularly with ferritic stainless steels. 

[bassmannate]

Here's an interesting link about using solder paste with SMD in a toaster oven!
http://www.seattlerobotics.org/encoder/200006/oven_art.htm