Author Topic: SMD prototyping techniques -- looking for advice  (Read 5734 times)

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Offline HB9EVI

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Re: SMD prototyping techniques -- looking for advice
« Reply #25 on: July 28, 2019, 10:19:40 am »
as being notoriously too lazy laying out and etching pcbs, I use dremel drilled islands for Rs, Cs, and transistors, dead bug for DIP chips and TSSOP/LQFP adapter boards in every needed combination; however I'm avoiding BGAs so far since the wiring is somehow suspicious to me, but maybe I change my opinion if there'll be no alternative to such a chip.

I do everything in that manner - from DC to lower GHz range
 

Online Siwastaja

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Re: SMD prototyping techniques -- looking for advice
« Reply #26 on: July 28, 2019, 10:34:26 am »
The smallest TH resistors (with thinnest leads possible) are great for SMD bodges, because they double as a resistor and wire. Much quicker to solder than an SMD resistor, then a wire to it.

But often you don't have small enough TH parts available.
 

Offline poorchava

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Re: SMD prototyping techniques -- looking for advice
« Reply #27 on: July 29, 2019, 02:00:08 pm »
In the company where i work we often have weird-shaped boards, so we can add protoboards on the waste areas of the panel. We literally have like 100kg of protoboards at hand :).

Privately, I use something similar to what Mike Harrison (mikeselectricstuff) is selling: http://www.whitewing.co.uk/protoboard.html
I love the smell of FR4 in the morning!
 
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Offline mark03

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Re: SMD prototyping techniques -- looking for advice
« Reply #28 on: July 29, 2019, 06:25:36 pm »
This is a deadbug technique I'm experimenting with. I have more pictures and details on my doc page at:
 https://mecrisp-stellaris-folkdoc.sourceforge.io/prototyping.html#prototyping

Tempted to draw an analogy between this and programming in Forth, but I won't  >:D

Seriously, that is impressive.  You have way more patience than I.

On the main topic, I may be lucky, but I almost always prototype with a custom PCB and some common-sense measures like extra pads, etc.  I can only think of one "coaster" I've made out of a couple dozen boards.  It's the rare case that can't be reworked with some bodge wires and creativity.
« Last Edit: July 29, 2019, 06:28:08 pm by mark03 »
 

Offline ogden

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Re: SMD prototyping techniques -- looking for advice
« Reply #29 on: July 29, 2019, 08:28:38 pm »
Tempted to draw an analogy between this and programming in Forth, but I won't  >:D

LOL :) Building miniature ships in a bottle is another analogy that comes into mind. Someone who is doing deadbug for >200pin circuit that includes 0.5mm pitch chips, clearly do not value his time.

 

Offline techman-001

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Re: SMD prototyping techniques -- looking for advice
« Reply #30 on: July 29, 2019, 08:36:47 pm »
This is a deadbug technique I'm experimenting with. I have more pictures and details on my doc page at:
 https://mecrisp-stellaris-folkdoc.sourceforge.io/prototyping.html#prototyping

Tempted to draw an analogy between this and programming in Forth, but I won't  >:D

Seriously, that is impressive.  You have way more patience than I.

On the main topic, I may be lucky, but I almost always prototype with a custom PCB and some common-sense measures like extra pads, etc.  I can only think of one "coaster" I've made out of a couple dozen boards.  It's the rare case that can't be reworked with some bodge wires and creativity.

Hahahah, some real Forth humor at last  :)

It does require a 20 - 40 x  microscope and steady hands ... but not that steady as I'm 65 years old.

This is a experiment leading into much more interesting possibilities. For instance, BGA MCU's can be very cheap indeed compared to the leaded versions, in fact I paid $0.45 each for the STM32L053 chips in that picture. They have the memory below plus all the M0+ low power peripherals :

­ 64 KB Flash memory with ECC
­ 8KB RAM
­ 2 KB of data EEPROM with ECC
­ 20-byte backup register

Just because a tiny BGA chip has 64 pins doesn't mean one has to use or even connect to them all ;-)

Imagine if one only needed 4 I/O's for a miniature project ?
 

Offline nigelwright7557

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Re: SMD prototyping techniques -- looking for advice
« Reply #31 on: July 30, 2019, 11:57:36 pm »
I design usb scopes as a hobby for the development experience.
My first design was 460K samples per second and all through hole.
Once I got up to 2MHz samples I found I needed to use SMD TQFP 0.5mm pitch PIC microcontrollers but I kept the rest through hole for ease of building.
My first attempt wasn't good as I bent a couple PIC pins being to rough and had to bin that attempt.
On the next attempt I was more careful and got the PIC lined up as spot on as I could then applied some solder.
I then put plenty of solder on the other 3 sides, way too much really.
I then found with plenty of liquid flux and a copper braid I could remove most of the solder. I found the trick was t ohold braid on the pins and move soldering along the braid so it didn't bend pins.
I put the PIC on its own small PCB that had through hole connectors to the motherboard.
Through the connector pads  I could buzz the pins out for adjacent shorts.
In fact in some cases a short didn't matter as both pins were inputs and not used.
I have built 3 pcb's now and they work great.

 

Offline ludzinc

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Re: SMD prototyping techniques -- looking for advice
« Reply #32 on: August 02, 2019, 01:11:14 pm »
Oh god that board is atrocious!
 

Online ebastlerTopic starter

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Re: SMD prototyping techniques -- looking for advice
« Reply #33 on: August 02, 2019, 03:05:15 pm »
@ludzinc: Your comments comes across as judgmental and derogatory. It is also quite unhelpful since you don't say what is wrong with nigelwright's layout.

Personally, I would route the tracks symmetrically and at 45° and 90° angles, but really that's mostly to satisfy my OCD. I am pretty sure the electrons will happily flow in arbitrary directions. ;)  And I would probably use SMD caps and quartz and place them on the bottom of the PCB, which avoids interference with the routing on the top and gets them closer to the processor chip. But since the adapter is meant to go onto a breadboard with further (longish?) external wires, we can assume that it is meant to work at clock rates where the exact placement of the caps is not critical.

Are there other aspects of the layout one shoud be concerned about?
 

Offline KL27x

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Re: SMD prototyping techniques -- looking for advice
« Reply #34 on: August 02, 2019, 10:23:58 pm »
That wouldn't work very well on a breadboard. Gotta do SIP or DIP for breadboard. Quad pack, no good. this board is obviously for:
 
Quote
I put the PIC on its own small PCB that had through hole connectors to the motherboard.

The only obvious things with this board, to me, are lack of ground plane and the trace width and routing. Trace width probably a mil or 2 smaller than necessary. And the arbitrary angles do not help with the PCB etch. The size of the gaps in the copper should not get too large compared to the trace size. I try to keep the gaps around a small trace to be roughly same thickness as the trace to maybe only 50% thicker. An easy way to fix this is to just use a top pour and set the gap/clearance as desired.

Of course if you are only ordering a small amount, it doesn't matter. You pay based on a formula that doesn't include this stuff. The fab will obviously make extras and throw away the excess, including the ones that fail. At some point of high volume order, your fab might actually make suggestions to increase the yield. Tiny traces with large empty space around them tend to break when you etch the board.

This might seem totally counterintuitive. You might think adding the top pour would near double the areas that could bridge and that the larger the clearances the better. But it's just not so. The areas right next to traces/pads is etched away, first, due to turbulence from the resist. Large empty spaces take the longest time to etch away, and during this time while waiting for them to clear, the traces are undercutting themselves.

« Last Edit: August 02, 2019, 11:25:55 pm by KL27x »
 

Offline Someone

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Re: SMD prototyping techniques -- looking for advice
« Reply #35 on: August 02, 2019, 11:49:20 pm »
Surprisingly, no votes for dedicated SMD protoboards, unless I overlooked something. That's great information -- exactly the kind of practical feedback I was hoping for.
The SMD pitch prototype boards are great but only if you have chips matching their spacing, for more complex prototypes you quickly end up with more than one pin pitch and it gets hard to do anything other than dead bug. But they are still a great starting base:
https://www.digikey.com/product-detail/en/vector-electronics/8021/V2017-ND/565946
 

Offline Unixon

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Re: SMD prototyping techniques -- looking for advice
« Reply #36 on: August 03, 2019, 08:47:20 am »
I would suggest to use a totally different approach to SMD vs TH.
TH prototyping is efficient at component-level, while SMD prototyping is not, SMD becomes efficient at least at module-level.
Therefore, it is much better to organize the entire workflow in a different way:

1) Establish a continuous project queue/conveyor. Now you will have to design, assemble and test different boards at a time, forget about working on a single project.
2) Design simple modules that include an IC and all requisite parts to get it working. Buy SMD-TH adapters where appropriate.
3) Keep sending boards to manufacturing and don't rely on quick turnaround, just switch to next task.
4) Assemble project from these self-sustaining modules, not raw parts, this is no longer the way.
5) Think about a "standard" form-factor and interconnect for your modules.

You will feel much more comfortable working with SMD when you'll have enough basic building blocks to assemble all you want and all design stages filled with sub-projects.
 

Offline nigelwright7557

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Re: SMD prototyping techniques -- looking for advice
« Reply #37 on: August 03, 2019, 11:55:35 am »
That pcb was routed pre making changes to my pcbcad software.
The problem was "off grid" SMD pins.
The software can now align track backwards to previous pin and forward to next pin.
This gives a much cleaner layout.
The pcb works absolutely fine at 200MHz, have three working systems.
Most of the i/o signals are low speed anyway.

The crystal and its caps and decoupling is close to the PIC on the pcb so thats major hurdles dealt with.
After that the I/o is simply 3 lines to a 74hc4051 and the rest to power rails.
« Last Edit: August 04, 2019, 05:13:36 am by nigelwright7557 »
 

Online nali

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Re: SMD prototyping techniques -- looking for advice
« Reply #38 on: August 03, 2019, 12:40:02 pm »
A bit of a mixture for me. Normally I'll go straight to PCB as proto PCBs are cheap or quick enough now (unfortunately never both!). Putting 0R resistors in signal lines can be pretty handy as they offer scoping points and breakout pads if something went wrong and you need to do some wire bodges.

Anything I'm really not sure about I'll invest in a manufacturer's eval board.

Also, for low speed breadboard these save the faff of soldering to adapters
https://images.app.goo.gl/kAgmN6Xfw7uGsEcC9


 

Offline nigelwright7557

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Re: SMD prototyping techniques -- looking for advice
« Reply #39 on: August 04, 2019, 05:15:11 am »
A bit of a mixture for me. Normally I'll go straight to PCB as proto PCBs are cheap or quick enough now (unfortunately never both!). Putting 0R resistors in signal lines can be pretty handy as they offer scoping points and breakout pads if something went wrong and you need to do some wire bodges.

Anything I'm really not sure about I'll invest in a manufacturer's eval board.

Also, for low speed breadboard these save the faff of soldering to adapters
https://images.app.goo.gl/kAgmN6Xfw7uGsEcC9

I thought about using one of those but I needed decoupling and crystal right next to the processor.
The processor runs at 200MHz so is fussy about decoupling.
 


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