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Smallest practical SMD size for etched boards? #pcbgcode


John Ferguson
 

I find I need to do a two sided board with some resistors and caps.  It looks like 1206 might be usable.  Is there any experience with anything smaller, or is even 1206 too small?

I have a reflow oven but so far have done all my soldering by hand


john ferguson


karmannelectric
 

I've done 0603 without too much trouble but for home milled boards I
prefer 0805. I wouldn't run a trace between the pads though (not that
I've tried; I'm worried about solder shorts without a solder mask) but I
bet you could with a 1206.
- Steve

I find I need to do a two sided board with some resistors and caps.  It
looks like 1206 might be usable.  Is there any experience with anything
smaller, or is even 1206 too small?

I have a reflow oven but so far have done all my soldering by hand


john ferguson






harry0099@...
 
Edited

Hi John,

if you use a v-bit with narrow tip (e.g 0.2 or even 0.1 mm) and a decent angle (e.g 10..30°), there is - or at least I see - no reason why you shouldn't use even smaller SMD parts.
I once did a design, two sided, too, with, I think it's 0603 parts and a 4x4 mm QFN chip. The linked page is in german, but there is a translation feature at the bottom of the page.

Harald


John Ferguson
 

Harry, that is very impressive work.  thanks for the link. 

john

On 8/10/20 11:00 AM, harry0099@... wrote:
Hi John,

if you use a v-bit with narrow tip (e.g 0.2 or even 0.1 mm) and a decent angle (e.g 10..30°), there is - or at least I see - no reason why you shouldn't use even smaller SMD parts.
I once did a design, two sided, too, with 0402 parts and a 4x4 mm QFN chip. The linked page is in german, but there is a translation feature at the bottom of the page.

Harald


peterg1000
 
Edited

Hi John,

No reason to avoid the 0603 components if your router is good to 0.001 - 0.002".  I use a V bit with a 30deg angle and a calibrated minimum isolation of 0.29mm - or just under 0.012" at a milling depth of 0.005".  The particular one I favour ( from StoneyCNC )leaves smooth edges to the etched lines - 0.2mm or 0.3mm endmills have all proven unsatisfactory, leaving rough frayed edges to the tracks.  V bits from China are dirt cheap and totally useless - frayed edges and unpredictable calibrated track widths - don't even pick up your barge pole!!

You'll need a means of getting your FR4 absolutely flat for this to work - I use a homemade vacuum table milled flat in situ for this.  I either use a vacuum pump or if convenient, very thin double sided tape to attach the workpiece and use a homemade touch probe to establish Z = 0 for each tool I use (repeatability is better than 0.0005").

Getting the correct ( VERY small) amount of solder paste has been the biggest challenge - and my latest experiment using a solder mask cut from 0.3mm mylar sheet is still under way.  As an alternative I've used a very fine hypodermic needle ( 25 gauge ) as a "trowel" to transfer from a bead of solder paste on a piece of siliconised paper to a solder pad. Its tedious in the extreme so I hope the solder mask experiment works. 

I've some pics of the latest effort, but have no idea of how to get this into a post - if it's even possible

With double sided boards,  vias are drilled to 1/32" and I then use 1/32" brass rivets (model engineering supplies) to join the tracks.  When purchased these rivets are usually well oxidised, so I soak overnight in "Clock Cleaning Solution" to get them bright and shiny. Handle with tweezers to avoid contamination.

Peter


Harvey White
 

I do double sided boards, 1206 and 805.  805 makes the layouts a bit easier in terms of parts packing.  I've used 608, but they get pickier about hand soldering.

Harvey

On 8/10/2020 10:18 AM, John Ferguson via groups.io wrote:
I find I need to do a two sided board with some resistors and caps.  It looks like 1206 might be usable.  Is there any experience with anything smaller, or is even 1206 too small?

I have a reflow oven but so far have done all my soldering by hand


john ferguson





John Ferguson
 

Thanks much gentlemen.

the specs for what I want to do show 805.s I'll try them.

best,

john