Svart

Re: SMD?
« Reply #20 on: December 15, 2008, 12:33:51 AM »
Quote
What are people using for critical film capacitors in audio band EQ circuits and such

PPS caps?  I have some but never tried them out.  I don't think they come in smd though.
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Andy Peters

Re: SMD?
« Reply #21 on: December 15, 2008, 01:49:22 PM »
I used a stainless steel stencil to apply solder paste, then put all the parts down with tweezers. After that I reflowed the solder on a hot plate. The process went reasonably well, and I'm working on streamlining it as I need to build a dozen more. There are over 60 line items (ie unique part/value combos) on both boards; sorting through these takes a considerable fraction of the build time.

Advanced Circuits (4pcb.com) offers "Benchtop" stencils for not-a-lot of money (http://4pcb.com/smtstencils/). We keep threatening to try 'em here at day-job for some of the more-complicated protos we build.

We have a kit of 1 mm and 1.27 mm BGA stencils that our ace assembly techs use to attach BGAs to boards. They use a hot-air nozzle above the work and a heater block below the work. They use a stereoscope to look at the balls on edge of the package while heating it, and it's "done" when they see the ball melt and the package sinks a bit.

After doing this kinda stuff for about five years, they've got a pretty-close to 100% success rate. This is important because every board we do has at least one BGA-package FPGA on it.

-a
"On the Internet, nobody can hear you mix a band"

mwkeene

Re: SMD?
« Reply #22 on: December 15, 2008, 09:58:49 PM »
Quote
PPS caps?  I have some but never tried them out.  I don't think they come in smd though.

AVX makes PPS in SMD http://www.avx.com/docs/Catalogs/cb-pps.pdf.  I think WIMA and Panasonic do as well

Quote
+1

I recall when we first started using SMT years ago in mixers and the immediate benefit to mic preamp layouts due to reduced loop area for sensitive circuits. You could just about fit the mic pramp under the input XLR. Back in the early days it was difficult to get some of the low noise transistors in SMT packages, because they were relatively large die for small signal transistors, but it was all worked out.

I don't have as warm and fuzzy feeling for SMT film caps, but maybe that has improved too... I had one bad experience with a small CM where the reflow temps affected the film caps, I tried to use. Ended up changing to a more robust part.

This is not new, the old polystyrene caps were not factory friendly for through hole.

JR

I've had these problems very recently so I'd say nothing has changed... The film SMD caps are very temperature sensitive.  We've experienced problems with the outer coating "shrinking" when too much  heat is applied via SMT oven or iron.  This can render the capacitor basically useless. 

-Mike
« Last Edit: December 15, 2008, 10:03:00 PM by mwkeene »

Rochey

Re: SMD?
« Reply #23 on: December 07, 2009, 03:25:05 PM »
Gents,

saw this video today, and wanted to share it with you.
http://www.youtube.com/watch?v=_5lksMvmqQc

"amazing" accuracy isn't needed when soldering on the skillet :)
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JohnRoberts

Re: SMD?
« Reply #24 on: December 07, 2009, 05:02:38 PM »
Yup.. even in the video you can see a few solder bridges still left, but they can be cleaned up with some solder wick, flux, and heat...  It wasn't as scary as I had feared.

JR

It's nice to be nice....

radiance

Re: SMD?
« Reply #25 on: December 08, 2009, 06:22:20 AM »

"amazing" accuracy isn't needed when soldering on the skillet :)

...  just whack some solder paste on it and go for a quick beer. Maybe put a pizza in the oven as well.... watch the olives when they align them self to the mozzarella.
"Knowing that you are dreaming, however, does not automatically guarantee full rationality.
Then again, being awake doesn't ensure good thinking, either." -  Lynne Levitan

mr coffee

Re: SMD?
« Reply #26 on: December 11, 2009, 11:14:17 AM »
Did y'all do SMD like these *without* solder mask on the boards? I can't tell from the pics.

JohnRoberts

Re: SMD?
« Reply #27 on: December 11, 2009, 11:29:31 AM »
I did one by hand applying the solder paste using a syringe. I was sloppy and while it worked fine for the low pin count larger devices, because of their lead spacing, I had lots of bridging on the smaller (resistor arrays) and high pin count devices.

While a bit of a struggle to get my technique down, some flux and copper braid, can wick away all the excess solder.

I did mine in my kitchen oven, temperature/timing was not very precise, but it worked well enough. I wouldn't rule out tack soldering a corner lead, or leads of a larger device, and would be careful about shaking or handling the PCB while solder is liquid.   

JR
It's nice to be nice....


 

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