SMD Soldering Question

[Govmnt_Lacky]

What do you use to clean the flux from the PCBs? I tried alcohol but... it just spread the flux all over into a sticky mess 

[CodeMonk]

This is what I used to do ages ago when I worked in the industry doing SMD stuff, mainly IC's.
I would files a groove in the end of the soldering iron tip.
This way I made contact on the IC legs and the pads at the same time...



I think someone on some forum posted a link to a tip similar to this.
Back then (1987 or so) I had to make my own.

[pickdropper]

dont forget simple tips
http://runawaybrainz.blogspot.com/2014/05/macgyver-smd-soldering-iron-adaptor.html
and drag soldering if you not have needle solder like Mr Pickdropper

Peace Mr Pickdropper 

No offense taken here.  There are many ways to get the job done.  I'll do the drag method on rare occasions, but it usually isn't my preferred method.  On some very fine pitch connectors it works better, however.

A lot of folks like the "flood and suck" method but it's always seemed like more work to me and I can do better soldering straight up.  YMMV.

[pickdropper]

What do you use to clean the flux from the PCBs? I tried alcohol but... it just spread the flux all over into a sticky mess 

Flux remover works better than alcohol.  You can get a board clean with high purity isopropanol, but it takes a lot of passes.  One or two passes will just leave it sticky (as you've observed).

I usually get the majority off with flux remover then switch to isopropanol.  I could do it all with flux remover but it's much more expensive and I've found a balance of the two that works for me.

[bloxstompboxes]

I use 99% isopropyl alcohol on boards we're given permission to use it on by the client, but we have the flux remover stuff too. However, I like the alcohol, a brush, and an airhose the best. I can get it cleaner than I can with the flux remover pen. I think it's all personal preference.

[vigilante397]

I recently had to remove an IC from an SMD board as I was under the impression I had mounted it upside down. I had a spare and didn't want to risk messing up anything else on the board so I clipped all the pins with flush-cut fingernail clippers and removed the remaining leads from the board one at a time.

Unfortunately, mounting the spare IC the other way still yielded no result On those lines, does anyone know how to tell directionality of a TL074? They don't have the indentation or the dot like through-hole ones do, and I'm fighting an uphill battle trying to debug a Hall Spawn reverb (courtesy of Pcikdropper himself) and I feel silly asking for help because I'm not even sure which way my IC should be facing

[slacker]

See if one of the edges is bevelled, that should be the pin 1 side.

[pickdropper]

The best thing for chip orientation is to check the data sheet on the chip you have.  Usually you can tell where pin 1 is, but occasionally it's necessary to get the info directly from the source.

If you send a picture, I can probably tell you if its facing the right direction on that particular board.

[Govmnt_Lacky]

I have found that "MOST" SMD chips are oriented with Pin 1 on the lower left when looking at the writing from left to right.



In this image... Pin 1 is on the lower left side. (directly below the "ST"

[slacker]

Yeah that seems to be the general rule. That pic also nicely shows the beveled edge I mentioned earlier.

[vigilante397]

I have found that "MOST" SMD chips are oriented with Pin 1 on the lower left when looking at the writing from left to right.



In this image... Pin 1 is on the lower left side. (directly below the "ST"

That does illustrate it very well. I had seen mention of the beveled edge but I guess I didn't know what I was looking for on the IC itself, but this shows it very clearly. I shall take a look when I get home from school this afternoon. Thanks

[vigilante397]

Okay, I checked when I got home and from the right angle I was able to notice the beveled edge. Assuming the beveled edge has pins 1-7 (it's a TL074CD) then it was oriented incorrectly before but I have it the right way now. Unfortunately it isn't working Would anyone be offended if I hijacked my own thread, posted some voltages and turned it into a debugging thread?

[Govmnt_Lacky]

Assuming the beveled edge has pins 1-7 (it's a TL074CD)

Do any of the SHORT sides have a beveled edge?



Different part number BUT.... look at how only one of the short sides is beveled. That indicates the chip header or top.

If you are using a TI chip then you can tell where Pin 1 is by the stamp on it. It is according to what I posted above. If reading from left to right, Pin 1 is on the lower left.

[vigilante397]

Do any of the SHORT sides have a beveled edge?

They do not, which is what I initially looked for and precisely why I didn't find it. And unfortunately they aren't the TI version so I can't refer to the stamp either.

The circuit is one that I can find absolutely no information about, which makes debugging a little difficult, but I took voltage readings today and based on the pinout found on the datasheet I believe I had it oriented right the first time and in fact have it backwards now The voltages I'm getting are as follows:

1 - 4.60        14 - 1.40
2 - 4.60        13 - 1.41
3 - 4.60        12 - 1.04
4 - 0           11 - 9.22
5 - 2.15      10 - 4.61
6 - 2.97       9 - 4.61
7 - 1.35       8 - 4.61

This makes me suspicious because V+ (9.22) should be on pin 4 and V- (0) should be on pin 11.

Someone please confirm my assumption for me

[Govmnt_Lacky]

This makes me suspicious because V+ (9.22) should be on pin 4 and V- (0) should be on pin 11.

Yep! You are correct that these voltages are on the WRONG pins 

Looks like its backwards.

[vigilante397]

Yep! You are correct that these voltages are on the WRONG pins 

Looks like its backwards.

Excellent The good news is I snagged a killer deal on a batch of 25 surface mount TL074's on the bay yesterday but this is the only build I have "so far" that uses them, so I can fry as many as I want as long as I get this working

[Govmnt_Lacky]

Excellent The good news is I snagged a killer deal on a batch of 25 surface mount TL074's on the bay yesterday but this is the only build I have "so far" that uses them, so I can fry as many as I want as long as I get this working

Just take your time. Remember... a lot of the pictures you see here of SMD builds are done by those that have proper SMD tools and experience. I just finished putting the last component on an SMD board myself and it looks nowhere near as good as some of the offerings I have seen here but, then again... I just had an oversized iron and some solder so I am pretty thrilled that it all went together. Just need to test it out 

Good Luck finishing up your build! 

[snowbird]

Almost every thing today is done with lead free solder. It takes more heat and the joints will not be as shiny.

You need several things to solder SMT.

1, FLUX, not just the stuff in the solder. Someone mentioned this earlier. Buy a good water soluble flux, such as the Kester that was mentioned earlier. Don't worry if you use too much, but make sure the boards are washed very well afterwards. Don't leave flux on your board overnight. If you are not done, wash and start over with more flux the next time you start.

2. Good solder. I would stay away from no clean (except for repairs or adding parts that can't be water washed later). I like .020 gauge.

3. Buy a good iron, not the wood burning iron you add as a kid. Good irons are a bit expensive. The Blue & Yellow Hakkos are one of the best values.  Keep you tips clean during soldering and don't use them forever. They will not last as long as the tin-lead solder either.

4. You need vision. A microscope is very helpful. As you get older, you will need more light. I think most people have better hands that vision when it comes to soldering SMT.



5. Soldering a pad for one side of a part is a common technique. You then slide your passive component while you heat up the joint. Tweezers work very well for this. I like the curved type best. Once the part is tacked down, solder the other side (LOTS of FLUX). Then reflow the first joint again to make it look better.  It will not look like joint created by solder paste and a reflow oven. You will almost always use more solder.

6. Soldering ICs is a little trickier. It's kind of like controlled bridging. Did I mention that you should use FLUX?

With a little practice, you will find that SMT is not really harder, just a bit different. One more thing - if you fabricate your own boards, I suggest ENIG. The parts lay flatter and the board doesn't tarnish. They cost about 10% more. Avoid HASL or tin plating.

Al

[Jdansti]

>4. You need vision. A microscope is very helpful. As you get older, you will need more light. I think most people have better hands that vision when it comes to soldering SMT.

What is the minimum working distance spec for a microscope?  Would 2-1/8" be enough?  Here's an example scope: http://www.amazon.com/AmScope-SE305R-PZ-Microscope-Magnification-Objectives/dp/B004SQQCHC/ref=lp_393248011_1_4?s=photo&ie=UTF8&qid=1427781276&sr=1-4

[snowbird]

The one you pointed to is more of a high school biology scope.

The Amscopes are great values. I own a bunch of them. Definitely better than an old Bausch & Lomb.

Here is the basic style that works well:

http://www.amazon.com/AmScope-SM-3BZ-80S-Microscope-Magnification-Ring-Style/dp/B006QN5T5G/ref=sr_1_7?s=electronics&ie=UTF8&qid=1427840903&sr=1-7&keywords=amscope

You want a long focus distance. For soldering 7-10x is usually about right, Occasionally you will use the higher zooms for inspection. This could be 50x.  The LED light rings are excellent. Better than the older fiber optic light sources and these are now cheap. There are a few choices but they are more the same than different. They are in the $400-$500 range though. You don't need 90x

There are a lot of used scopes available. These often go with stands for $300 or so. I have seen them at ham swap meets, etc.  Don't buy a scope without a stand. Sometimes the stands are harder to find than the scope. The fittings vary from one type to another so make sure you have a good functional pairing. Also look through the scope. Sometimes they are damaged. I have also seen a few without eyepieces, not so useful....

I solder through hole with a microscope as well -- maybe its my age catching up. You learn fairly fast where your hands are. I don't think I have burned my fingers for several years, but there is a very good feedback mechanism as you start out.