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Author Topic: Correct Solder Temperature for SMD Components?  (Read 7315 times)
AB0RE
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« on: February 25, 2013, 08:38:11 PM »

Hello,

I need to replace a few surface-mount chip-style capacitors and resistors on a project here.  I'm attempting to determine the correct soldering temperature.  My soldering station is a WES50 that does 350 - 850 degrees Fahrenheit and I'd likely be using either the "ETO" .8mm long conical tip or "ETS" .4mm long conical tip.  My solder is Kester "44" rosin core solder, .031" diameter.

I've searched for the answer online but have been finding numerous different answers to this question, most answers being in the 500 - 700 degree F range.  Sure, I could try different temperature ranges and find what works best, but I'd rather cut down on the learning curve by listening to advice from those of you who have experience soldering Surface Mount components.  Is a higher temperature preferred with less time with the soldering iron on the pad/component?  Or is a lower temperature needed?

Thanks & 73,
Dan / ab0re
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VK2TIL
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« Reply #1 on: February 26, 2013, 12:51:41 AM »

I think that "quick in & out" is the key to all good soldering, SMD or otherwise; you should make the joint in the time it takes to count "one".

I use 350C on my station for leaded-device or SMD soldering.

I also think that using a tiny tip isn't the best way; use a small tip but one that has a bit of mass and holds some heat.  The needle-pointed tips aren't good at transferring heat to the joint; use a chisel-tip or a wedge-tip.

The tip is like a reservoir; it has to hold some heat for transfer to the joint.  The heating element is only for heating the tip; if you are relying on the element to heat the joint you will have a poor joint.

A pointed tip has little interface area between the tip and the joint so heat transfers slowly; a tip with a small flat surface transfers heat much more quickly.

Solder paste is good; Cash Olsen sells it at cost in small quantities.

But Kester 44 is great; I use it a lot.

Just remember; fast-in, fast-out!

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KE3WD
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« Reply #2 on: February 26, 2013, 05:47:02 AM »

That's good advice. 

I'd only add this:  Don't fixate on the temperature gauge other than to use it to make sure you aren't in the higher temperature region that can cause delamination of the copper traces.  Instead, watch the solder melt and flow action, which will "talk" to you about a good temp setting within those 500 to 750 or so parameters. 

The Eutectic 63/37 solder, in the smaller diameters, is what I like to use. 


73
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W8JX
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« Reply #3 on: February 26, 2013, 08:06:59 AM »

Try 600 degrees. If you go much colder you can get a cold joint because soldering cools tip some until it recovers. The "trick" is you have enough heat without being excessive to get on and off joint quickly. Technique plays a roll here too.
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K5LXP
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« Reply #4 on: February 26, 2013, 10:19:10 AM »

Liquid rosin flux is your friend.


Mark K5LXP
Albuquerque, NM
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W8JX
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« Reply #5 on: February 26, 2013, 10:38:48 AM »

Liquid rosin flux is your friend.

Actually not. Less flux the better as it is no substitute for improperly cleaned surfaces. Many many years ago I took a NASA sponsored high reliability soldering course by my employer at the time. Liquid flux was a forbidden.
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KB4QAA
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« Reply #6 on: February 26, 2013, 10:47:33 AM »

In  my experience the Nasa/military standard is 700F.

Liquid solder flux can make a big difference in ease and quality of soldering, particularly if you are doing rework on old components.

There are 'cheap' and even 'bad' solders out their.  I was given a kit to build which came with solder and so help me, I couldn't get it to stick for love nor money.  Radio Shack solder has always been at least decent, but I got a roll that had some punky rosin.  Ick.   Kester 44 is pretty much the gold standard for solder.

Keep your tip clean.  Have either a wet sponge or a brass scrubber beside your stand and use them regularly.  Wipe clean before going to the work, and put a little solder on before setting the iron down in the stand to keep it covered against oxidation.  

bill
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KB4QAA
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« Reply #7 on: February 26, 2013, 11:04:08 AM »

http://snebulos.mit.edu/projects/reference/NASA-Generic/NASA-STD-8739-3-2.pdf

NASA soldering standards, 1997

And yes, liquid flux is allowed.
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W8JX
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« Reply #8 on: February 26, 2013, 12:21:54 PM »

http://snebulos.mit.edu/projects/reference/NASA-Generic/NASA-STD-8739-3-2.pdf

NASA soldering standards, 1997

And yes, liquid flux is allowed.

Well I went well before 97 and it was not allowed then. They were heavy on cleaning before and after soldering. Any leftover flux is potentially corrosive over time an less used the better.
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W6EM
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« Reply #9 on: February 26, 2013, 09:15:03 PM »

Most of the liquid flux pens available now claim to be non-contaminating.  For doing SMD rework or whatever, the liquid is a must.  Makes the time needed to melt, tin and flow extremely short.

I did some eeprom replacement on some SMD boards and I used a heat gun with a home-brewed copper heat shield to keep the hot air off of components I didn't want to remove.  This worked quite well as the shield had a window over the component I wanted to replace.  The replacement was lightly clamped in place, and with liquid flux, I was able to quickly tin and flow all sides of the new IC.  My Ungar pencil has a very small chisel tip and was set for about 600F.

The flux minimizes pin to pin shorts by speeding the tinning process along.  I used 15 mil 60/40, as I recall.  Either Kester or Alpha.

Lee
W6EM
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KE3WD
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« Reply #10 on: February 27, 2013, 07:07:10 AM »

Been prototyping boards, also repairing Surface Mount since it was introduced, in all these years I've never needed a separate Flux. 


Exception is the use of the fine ChipQuik product for removal of SMD devices, in this case the kit comes with its own syringe filled with their proprietary compound, which is a flux of sorts, but not the type used in electronics soldering, this stuff is designed for use with the ChipQuik desoldering alloy "blob".  Works very well and I recommend obtaining the ChipQuik kit to anyone delving off into the world of Surface Mount. 


73
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AJ4WC
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« Reply #11 on: February 27, 2013, 01:39:21 PM »

It cannot be done correctly with just a soldering iron and you risk damaging the circuit board.  Rosin core solder is also verbotten.  The rosin acts like a slow motion acid that will damage the board.  In the early days of SMT, I removed and replaced many components with just an iron; however, as they have continued to get smaller, it's no longer practical.

To do it correctly, the board is warmed slowly with controlled temperatures, rather than fast and hot.  Typically, the underside of the board is warmed to just below the melting point of the solder, around 150C, then the component side is heated simultaneously and the components is removed, then there's a cool down period as well.  All this is done thru high magnification microscope with a mechanical mechanism to place the component in the exact position without displacing surrounding components.

If I could upload a 4 MB file, I would show you a Powerpoint presentation one of our staff did that shows how to do it properly with temperatures, etc.  Here's link to the machine we use with a video showing the machine in action: http://www.pdr-rework.com/node/69

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K5LXP
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« Reply #12 on: February 27, 2013, 03:19:48 PM »

It cannot be done correctly with just a soldering iron and you risk damaging the circuit board.  Rosin core solder is also verbotten.

Granted, a BGA R&R takes a bit more skill and equipment, but for a few R's and C's (and many other SMT devices) it's absolutely doable with an iron, or hot air and solder paste if you like.   

"Wrong" techniques are allowed - this is hobby/prototype stuff, not space qualified.


Mark K5LXP
Albuquerque, NM
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AB0RE
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« Reply #13 on: February 27, 2013, 03:42:31 PM »

Hello,

Thanks everybody for the comments / assistance offered.  The surface mount components were dang cheap from Digi-Key so I ordered plenty of extras, just in case I get a little too excited with the soldering iron.

VK2TIL - Excellent advice on the tip, thanks.  I have a "screwdriver" tip that I will probably end up using.  I failed to think about the importance of thermal mass when I thought about what tip to use.  I know this certainly does make a difference based on my experience soldering on PL259s.

I guess we'll put "flux" in the same category (controversial) as baluns and j-poles.  :-)  I have a flux pen and was thinking of wetting the pads before-hand but will also take note that flux is no substitute for a clean solder pad.  I also have a brass scrubber pad to keep the tip clean, as suggested.

AJ4WC - Thanks for the link to the video.  I'll put the machine on the Christmas list this year but I suspect Santa won't think I was *that* good.  I have noticed reading datasheets for some of these components that they recommend "pre-heating" the components as well.  Several of the sheets also suggest solder temperatures that doesn't exceed ~526F for no more than 5 seconds.

I guess the plan will be to maybe try ~500F and see how it works, adjusting hotter if it appears it is taking too long or I'm getting cold joints.

73,
Dan / ab0re
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W8JX
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« Reply #14 on: February 27, 2013, 08:58:37 PM »


I guess the plan will be to maybe try ~500F and see how it works, adjusting hotter if it appears it is taking too long or I'm getting cold joints.


Too cold. You have to remember that if a fine tip starts at say 600, it will quickly cool 50 to 75 degrees or more as you melt solder/flux and heat surfaces to take solder. Again you want enough heat to do it quickly and get off to minimize component heating. Using too low a temp will actual heat soak components more as it takes longer to heat joint properly. 
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