The ugly reality of the new frontier - are those PCBs feasible?

[Mark Hammer]

First, let me say how excited I am that digital hardware effects have gotten so close to being DIY-able.  Equally happy that there is enough of a critical mass to warrant a separate forum so that interested parties can find stuff in one place.

This particular stream involves a certain different type of expertise, which is learnable I suppose, and a certain component access which is also feasible.  But more critically, perhaps, it involves a certain physical scale of construction that many of us may not be able to achieve on our own. or that may involve paying greater attention to certain things than was needed previously for either DIP spaced or discrete component circuits.  Those damn chips are tiny and the traces are thin and crammed.

Is PnP usable for the sorts of boards that will need to be made, or is its resoluion insufficient?  Is it fine only if one uses a laser process of a certain resolution or better?  Is one etchant better than another?  Does it need to be fresher?

What kind of a soldering tip does one need?  Is there a model number?  Is there solder which is better for this purpose?

Is it time to start stocking up on 1/8W resistors to accommodate the spacing?

[Peter Snowberg]

Take a look at MetalGuy's layout for DaveTV's Femto-verb.

Most of the chips will be able to be soldered to "surfboards" or ready-made layout to get past the small component hurdle.

You do need a decent iron with a small tip, but not much beyond that and some liquid or paste rosin flux. A 20 or 25 watt iron should be great, but temperature controlled stations are just a zillion times better and can be had for $40 US.

If you get boards made from a PCB house, the solder coating works great to attach most components by simply re-flowing what solder is already there.

I don't use PnP so I can't answer that, but from what I see people do around here is looks like no sweat for chips with 0.05 inch lead spacing. You obviously want good conditions for clean etching, so fresher etchant may be more important than before. Idea: use the fresh stuff for smaller features and recycle for general boards.

For solder, I like small 63/37 solder for almost everything (including big connections).

Nothing says you need SMD parts for the rest of things (caps, resistors, transistors, etc.). SMD is REALLY EASY to deal with if you have liquid or paste flux.

Give it a try and I think you'll be pleasantly surprised by the ease of soldering.

I love working with surface mount parts.

[David]

Nothing says you need SMD parts for the rest of things (caps, resistors, transistors, etc.). SMD is REALLY EASY to deal with if you have liquid or paste flux.

Tell us more, Sensei...  tell us more...

[Peter Snowberg]

I use a Xytronics 137 iron with a very fine tip and fine solder. I also have paste flux and solder braid on hand. If you have good light and a steady hand, that's all it takes. Oh yes, it also helps to skip caffeine before.

Random Google results:
http://www.diyaudio.com/wiki/index.php?page=SurfaceMountDeviceRework
http://www.avrfreaks.net/index.php?module=dpDocs&func=display&mid=61
http://www.howardelectronics.com/chipquik/smdrepar.html
http://www.zeph.com/smd_solder_process.htm

Google will produce lots of results that talk about solder paste and hot air. What that's a better way to go, the old faithful Xytronics iron does GREAT. I also picked up the SMD tweezers for my iron and they're great.

[David]

Well, I've certainly got the hot air covered...   

Domo arigato, Sensei Snowberg...

[Peter Snowberg]

Dou itashimashite. 

[free electron]

I also use a lot of SMT parts in my pedals, practically all resistors, some caps (mostly power lines filtering), BJTs and IC's.
Here's an example: a pwm controlled phase/vibe i had written here about some months ago. Still requires some work, but only in software domain, it's not a problem since the device is "in circuit" programmable. The heart is the SOIC20 ATTINY26 atmel uC. the pcb is designed to fit into 1590BB enclosure.

And here's my Latching Relay true bypass module with anti-pop circuit:

I use 24W soldering station, forceps, sometimes mangnyfying glass when working with 0603 components. It's very easy, especially for someone who already has some experience with classic through-hole assembly.

[phaeton]

Just wanted to note that a lot of folks in an electronics irc channel I occasionally pester on freenode do nothing but SMT.  I don't think any of them do any audio circuits, but that's really immaterial.  They say that SMT is much easier to work with than you'd expect.   They just apply solder paste, arrange the components, and then after a ride in a thrift store toaster oven for about 20 minutes they're all done*.

In effect, this is supposed to actually be easier because you don't have to drill any holes or flip the board around as much.  Now all we need to do is get our buddy Steve at SmallBear to come up with some nice PCBs with "grid" lines on them- just cut traces to make your circuits





*note that you can never again use this toaster oven for food after baking a PCB in it.

[johngreene]

I've done a -lot- of prototyping with surface mount parts. For DIY boards I actually prefer it because it greatly reduces the amount of drilling needed. I find that it is easy to solder even really fine pitch parts if you have 3 things:

1. A magnifier (more so these days, dang eyes...)
2. liquid flux.
3. a fine tip iron

The real key is the liquid flux. You can place the chip with tweezers and apply liquid flux. Then just press on the pin with a -tinned- iron and enough solder will flow to make the connection. Once 2 pins are connected this way the tweezers are no longer needed and you can solder the rest of the pins easily. Use braid to clean up if you get too much solder. I've never used paste for prototyping.

Now BGA's are an entirely different story. I don't think there's a reliable way of soldering them by hand. At work we use a $25,000 station to work with BGA parts, and even then it isn't all that easy. Especially with lead free solder. Alignment is the tough part.

--john

[bioroids]

Hi!
What are the prices on SMD components, like resistors, caps, transistors and diodes, compared to the "standard" thru-hole counterparts?

In Argentina I think that only the resistors are cheaper, the rest is still more expensive on the SMD version. Is this tru for other countries?

Luck

Miguel

[David]

Dou itashimashite. 

I hope to hell that means "thank you" because I already used the sum total of my Japanese...

[Doug_H]

As for making your own PCB's... I suspect the PnP days will be over for many people in this area. It may be time to start relying more on places like ExpressPCB, for example, to get PCBs made for you. In addition, a pcb house can handle multilayer stuff, which you may be more prone to get into with dsp stuff.

Doug

[R.G.]

Yep, the PNP and sharpie marker days are over when you get to SMD.

One solution that works - if you can still find the machines - is to get one of the old pen plotters and plot with resistive ink directly on the PCB material. But that's not a general solution.

What has a lot more hope is making the PCB not matter. The reasoning goes like this.

- Microprocessors tend to hollow-out everything they touch. The end result, and the desirable, elegant one in the view of a uP designer is that there is NOTHING left of the original function except the user-visible controls and the uP.
- A DSP setup for effects, given only that it is reprogrammable, can do any audio effect within its power.
- DSP power increases by Moore's law, so more effects, and more simultaneous effects, become possible, doubling every 18 months

Therefore - what is desirable is the same PCB for every effect. It should have the DSP, a programming means, a means for controlling the effects from pots, switches, etc., and audio ins and outs. Other than that, it is not useful to have any analog stuff on the board at all. Since the DSP can do any effect you can program, all PCBs become the same, and the function is limited by DSP processing speed, not clever circuit design.

So what we want is a reprogrammable DSP that does good effects. After that, the task of making effects consists entirely of getting a board, always the same board, ideally already populated, and then programming.

It makes the boards really cheap. You do one board, make a zillion, and you're done.

Welcome to ... the Future...

[phaeton]

Agreed, R.G....

However, while programming has its fun, I think I enjoy the 'old fashioned' breadboarding and board assembly as such with discrete components.  I burned out on programming a few years ago, and in many cases I look forward to building audio circuits because it gets me away from the computer.

It's not that I'm trying to run away screaming from SMT or do the whole rose colored "but discrete transistors sound warmer than bitwise calculations and pointer bitbashing in C" thing....   I just find working with 'real' things I can pick up and touch and blow up by accident somehow 'therapeutic' after a long day of manipulating (or being manipulated by) abstract and intangible concepts and systems.

YMMV, and I'm not trying to be a buzzkill for this thread.  Honest Injun.

[Doug_H]

What has a lot more hope is making the PCB not matter.

Continuing the thought and probably restating a few things you said in a different way:

What we're really building here is a microcomputer platform in a pedal-sized box. What determines what *it* is are the particular control parameters (knobs), the cpu features, and the software. So, IMO it is not only good to collaborate on standard h/w (or sets of h/w) as Tom implied, it would be advantageous to agree on a common platform(s)- cpu, peripherals, pcb, etc as well.  Once you design/test a platform, you're done. PCB's etc can be copied, made available and so forth, and at that point as you say "the pcb doesn't matter".

One question I have, since I'm a newbie at dsp, is there any advantage to having a "development platform" vs. a "production platform"? IOW are there bells & whistles you need in the h/w during the development cycle that would be unnecessary/costly/ physically-restricting for deployment? I'm guessing not, since it seems like all you really need is a usb port to download code to test and then some flash to burn it in when you're ready to "save".

Doug

[Dave_B]

Yep, the PNP and sharpie marker days are over when you get to SMD.

Personally, I still prefer the old way of making boards.  In my experience there's no touch-up whatsoever using the photographic method and the high cost is overstated.  Here's a link showing the Polyphase board I started yesterday.  After printing the artwork, I had an etched board within 45 minutes.   

[R.G.]

In my experience there's no touch-up whatsoever using the photographic method and the high cost is overstated.

I quit doing PNP a long time ago because I was over its resolution limit. I use positive photo for everything at home. I built an exposure stand with two 24" fluorescents and a vacuum exposure tray for this. I get about 8 mil resolution.

After printing the artwork, I had an etched board within 45 minutes.

The etching is almost never the problem.

The drilling... now that's a problem. SMD boards offer you the opportunity to think of PCBs largely in term of avoiding vias... 

[Dave_B]

I use positive photo for everything at home. I built an exposure stand with two 24" fluorescents and a vacuum exposure tray for this. I get about 8 mil resolution.

Just curious, do you (or anyone who also does it this way) buy your boards presensitized or do you coat them yourself?  I've been buying ready-to-go boards for the last few years, but just last week bought the bottle of stuff to lacquer them myself.  I haven't tried it yet. 

SMD boards offer you the opportunity to think of PCBs largely in term of avoiding vias... 

As a charter member of the coffee generation, I'm not sure I'll ever be able to do SMD's.  My wife can solder them at competition speeds, but she has zero interest in helping me make more noise.   

[puretube]

PRE!

[johngreene]

I use positive photo for everything at home. I built an exposure stand with two 24" fluorescents and a vacuum exposure tray for this. I get about 8 mil resolution.

Just curious, do you (or anyone who also does it this way) buy your boards presensitized or do you coat them yourself?  I've been buying ready-to-go boards for the last few years, but just last week bought the bottle of stuff to lacquer them myself.  I haven't tried it yet. 

Presensitized is the way to go. Especially since they've improved the material about 6-7 years ago. The current photo-resist almost 'flashes' over after it is exposed the right amount of time. The old stuff would be more gradual so exposure time was more critical. I tried coating boards myself with very limited success. It's just not worth it and the cost savings does not justify the additional effort/care required.

--john