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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets.

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Old 21st Nov 2020, 3:45 pm   #21
60 oldjohn
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Default Re: SMD soldering

Hi Steve, Good luck with your soldering, everyone has their own method. I find using the tined flux (from Ebay 2.09 in Grey / red tin) is easiest. Using a piece of wire, cocktail stick or similar apply flux to pad then use same wire to pick up component (sticky) and place in position. I did try with tweezers only for the component to escape, never to be seen again.

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Old 21st Nov 2020, 3:54 pm   #22
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Default Re: SMD soldering

Something also worth noting is that SMD ceramic caps can go short-circuit due to thermal stress. Annoyingly, this can happen a while down the line (typically when the unit is in service...). If you are soldering them, do everything you can to minimise heat stress - short circuited caps can do a lot of damage!
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Old 21st Nov 2020, 4:03 pm   #23
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Originally Posted by knobtwiddler View Post
Something also worth noting is that SMD ceramic caps can go short-circuit due to thermal stress. Annoyingly, this can happen a while down the line (typically when the unit is in service...). If you are soldering them, do everything you can to minimise heat stress - short circuited caps can do a lot of damage!
I have had SMD caps go open circuit, actually breaking in two after a day or three, not sure if it is the capacitors, my soldering, or the thin PCB 0.7mm thick x 11m x11mm. The Ceramic caps can also be microphonic.

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Old 21st Nov 2020, 8:57 pm   #24
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Default Re: SMD soldering

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Quote:
Originally Posted by knobtwiddler View Post
Something also worth noting is that SMD ceramic caps can go short-circuit due to thermal stress. Annoyingly, this can happen a while down the line (typically when the unit is in service...). If you are soldering them, do everything you can to minimise heat stress - short circuited caps can do a lot of damage!
I have had SMD caps go open circuit, actually breaking in two after a day or three, not sure if it is the capacitors, my soldering, or the thin PCB 0.7mm thick x 11m x11mm. The Ceramic caps can also be microphonic.

John.
Consider yourself lucky! I have literally seen tens of them, from different brands, go short - when they've been hand soldered... On some occasions the PSU has soldiered on, without going into I-limiting, thus turning said cap / caps into charcoal. On other occasions the PSU's sensed the load and gone into protection. I've serviced items where the owner didn't think there was a fault, and I've seen blackened, crusty caps - looking like a dried insect.

I can't say 100% that the shorts weren't stress related. However, I find this implausible, considering how much abuse SMD caps get in modern gear such as phones and the like. Nor do I see how they'd get the physical abuse when soldered. My feeling is that they like a short, sharp soldering cycle - and beyond that can brew up trouble down the road.
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Old 21st Nov 2020, 9:11 pm   #25
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Default Re: SMD soldering

SMD seems an incredible tech advance to me. I am practicing my skills and enjoying the journey. When I consider the reductions in scale of passives as well as switches (esp power MOSFETs) I wonder what the future will look like.

I also note that this down-scaling of size vastly reduces stray inductance particularly and associated problems with circuits operating at colossal switching speeds.

I am curious to know from the experts how mass-production works, including the avoidance of thermal stress during soldering.
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Old 21st Nov 2020, 9:21 pm   #26
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Default Re: SMD soldering

They use little machines

This is most of one board assembly line.

You might want to watch this (music a bit poor though)

https://www.youtube.com/watch?v=t9Se56mFDFA

Cheers

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Old 21st Nov 2020, 9:35 pm   #27
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Default Re: SMD soldering

Wow!

J
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Old 21st Nov 2020, 9:40 pm   #28
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whaaaat, Mike? Did I see 39,000 components per hour? I don’t have any German so I can’t understand the text but I see the incredible reality of these robots doing their thing. What’s the soldering time ? It seems blisteringly fast.

I wonder what the inventor of the first monolithic audio amplifier (I only saw the ad. the other day for he first time in a vintage magazine ) and prolific circuit designer / publisher of the 1960’s to 70’s, Clive Sinclair, makes of all this?

Wow.
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Old 21st Nov 2020, 9:53 pm   #29
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Default Re: SMD soldering

Due to Covid I don't go over the factory as often as I used to but these machines are something else.

I was trying to find the video of the flow soldering part.

The first picture is actually part of the Siemens factory in Poole from the Mobility twitter feed.

I just noticed there is an English version of the placement machines.

https://www.youtube.com/watch?v=T_NQC5cmRRM

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Old 21st Nov 2020, 10:00 pm   #30
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Default Re: SMD soldering

Thanks for that version, Mike. I find this mind-blowing.

I have used an online service to make a board for me from a file I supplied but I had no idea of the reality. The scale of the robotics seems remarkable, just a few humans in the frame as millions of components an hour get picked and placed.

How did this all get designed?
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Old 21st Nov 2020, 11:10 pm   #31
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Default Re: SMD soldering

The limitation is the number of different part values each station can have threaded up at one time.

Designers have to limit the number of different resistor and capacitor values they use on a board. This can look wierd to people looking at diagrams downstream.

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Old 22nd Nov 2020, 10:42 am   #32
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Default Re: SMD soldering

Regarding the capacitors, it's a know issue and is known as capacitor cracking. Often caused by localised phsical stress on the component when the PCB is snapped out of it's panel or some other assembly process. In the case of this thread, it could be either thermal shock, mechanical handling, or uneven heating causing mechanical stress.

One customer we supplied insists that strain guages are put on a board in a panel after surface mount, and then run through the rest of the process to check a limit wasn't exceeded. They also have rules about having two MLCCs in series but mounted at right angles (so the chance of cracking both is minimised).

The issue occurs after a while, because it's caused by electromigration of the metal through the cracks in the ceramic, driven by the voltage applied. So it only really starts once the device is in service. It depends where in the circuit the cap in question lives and if it's one the main power in then you can have serious issues.

And I have seen it happen where an MLCC has gone short after initially testing good. The process had been strain gauged and passed. But without telling me the factory changed the process. Then they had loads of parts that had passed EoL but then failed while being reworked with new Firmware. Luckily that cap was on the output side of the Vreg so the current was limited, and just resulted in lots of dead parts. I'm glad that got caught before we shipped the first batch to the customer.
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Old 22nd Nov 2020, 10:51 am   #33
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Default Re: SMD soldering

One evil trick:

Turn a post-it note upside down on the bench. You can put SMT components down on its sticky strip and they won't blow around.

You can write values etc on the non sticky part with an arrow pointing at teh component.

David
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Old 22nd Nov 2020, 11:07 am   #34
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Default Re: SMD soldering

Great idea, David. I’ll give that a try!

Cheers
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Old 22nd Nov 2020, 12:18 pm   #35
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One evil trick:

Turn a post-it note upside down on the bench. You can put SMT components down on its sticky strip and they won't blow around.

David
Excellent tip!. Used it myself when I was having to fit a diode so small you could only see the marking onder a microscope. Why so small a diode? well the task was to left one leg of an SOP chip, and fit the diode between the chip leg and the PCB land.

I did have a few ping out of the tweezers. Couldn't tell them from the dirt once they had done that. I think I lost more than I soldered, probably by 2:1.
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Old 22nd Nov 2020, 12:25 pm   #36
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Default Re: SMD soldering

Might i make one more useful suggestion to add to your toolkit, I've always found a small brass wire brush very useful to clean the iron tip, something like an old hush puppies brush.
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Old 22nd Nov 2020, 12:59 pm   #37
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Default Re: SMD soldering

Resistors, useless put in upside down as you can't read the value, place on a bit of paper and a quick tap will flip them over randomly some will be the right way up. Also as most SM stuff is so cheap if you lose track of a component value/type, bin it and get a new one.
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Old 23rd Nov 2020, 1:01 am   #38
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Default Re: SMD soldering

Industrial tiddlywinks.

I sometimes surround my microscope area with clean, plain coloured card. Any pinged components show up well. Bench surfaces inevitably get marked and graunched-up like a mini battlefield. Even 0603 can hide quite well.

Metcal iron stands come with a scrunched-up brass pan-scourer shoved in a little pigeon hole for cleaning bits. Seems to work, and is supposed to avoid the thermal shock of a wet sponge on a very expensive bit.

One of the American QRPers had a cannery as a family business. He brought out a range of QRP kits in cans. Pull the tab, open the can and take out the components, then build the set using the can as the cabinet. The one I bought is the canned pan-scourer for cleaning soldering irons. He even sold canned underwear in case you got a nasty shock.

RS did a little tin of bit cleaner compound, seemingly a hard piece of solder paste/flux block. Worked brilliantly, but lead based so presumably the people responsible have been taken out and shot by the ROHS people.

David
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Old 23rd Nov 2020, 10:33 am   #39
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Industrial tiddlywinks.

RS did a little tin of bit cleaner compound, seemingly a hard piece of solder paste/flux block. Worked brilliantly, but lead based so presumably the people responsible have been taken out and shot by the ROHS people.

David
They still do, but now 'unleaded' as it were:

https://uk.rs-online.com/web/p/solde...ories/8183207/
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Old 23rd Nov 2020, 9:00 pm   #40
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Default Re: SMD soldering

Dont know if anyone noticed but I realised at some time in its life the magnifier has been disassembled and the head put back on upside down. Ive sorted it out. im struggling on the smallest parts in not getting too much solder on. May get a tub of solder paste and try it.
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