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methods for soldering .5mm pitch

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rp181

Fri Jan 15 2010, 10:45PM

Registered Member #1062 Joined: Tue Oct 16 2007, 02:01AM
Location:
Posts: 1529

Hello,
I have some 80 pin packages, .5mm pitch, in a Low profile quad flat package (LQFP).
I have two questions:
1)Are TQFP packages compatible with LQFP? In other words, can I use my LQFP package on this breakout:

2) How should I go about soldering these? Drag soldering seems like the best method so far. Will it work with conical tip? How slow do I go when dragging? Temperature I should use with leaded solder?

~Rp181

Mattski

Sat Jan 16 2010, 12:31AM

Registered Member #1792 Joined: Fri Oct 31 2008, 08:12PM
Location: University of California
Posts: 527

See:

The TQFP seems to be a bit bigger in outer dimensions, you might take a closer look at the datasheets, but I don't think it'll work well.

The dragging method is probably the best way without breaking out solder paste and a toaster oven. I usually solder lead solder around 650F, but it depends a lot on your station, how much heat goes through the traces and chip, what tip you use. Best is to start low, and only then crank it up if it doesn't flow smoothly. The speed you go at is just slow enough to get a pretty even coat of solder on the leads and pads. I like to run the iron so it's half on the pads, half on the leads, that way the bridges that form aren't right up against the package where they're hard to fix. And then when you're done, slather on some paste flux, put some liquid flux in your copper braid if you have it, and with a really hot iron run it quickly across the pads to remove bridges.

It's hard to teach this in words, or even in person, you really just need practice. If you got some broken electronics with similar chips, practice this beforehand. You can bridge the pins and develop a feel for effectively debridging them. It'll be hard to practice soldering it down though, since it's hard to take big chips off in one piece without the right equipment.

Also, when doing tricky soldering operations I sometimes pre-heat my board and component in a toaster oven to about 180F. That way you don't wasted a bunch of heat just getting it up from room temp. This is especially good when soldering ground connections. Wrap the whole thing in foil before you stick it in so you get more even heating.

Z28Fistergod

Sat Jan 16 2010, 04:43AM

Registered Member #2040 Joined: Fri Mar 20 2009, 10:13PM
Location: Fairfax VA
Posts: 180

I just did a board with some 0.5mm and 0.65mm components and the one thing I really wish I had was a decent microscope. I had bridges form that were impossible for me to see with the naked eye. All I had was a very cheap handheld "microscope" and I really hated it. One of those USB microscopes would have been perfect I think. I'll be getting one before I do another SMD board.

I also use the flooding technique, it seems to be the easiest for me. This page

has a very nice video that shows various techniques with various packages, and all using soldering iron.

rp181

Sat Jan 16 2010, 05:09AM

Registered Member #1062 Joined: Tue Oct 16 2007, 02:01AM
Location:
Posts: 1529

Thanks!
I looked at the datasheet for a 80 pin TQFP, the dimensions match (can someone varify for me?).

I think I am going to try drag soldering, then if I mess up on that, flood it.

I don't know how your eyes are, but It seems I can see the leads pretty distinctly without magnification (I am VERY near sighted, failed every single far sight test at the optometrist).

Z28Fistergod

Sun Jan 17 2010, 03:01AM

Registered Member #2040 Joined: Fri Mar 20 2009, 10:13PM
Location: Fairfax VA
Posts: 180

rp181 wrote ...

...
I don't know how your eyes are, but It seems I can see the leads pretty distinctly without magnification (I am VERY near sighted, failed every single far sight test at the optometrist).

Near sightedness is perfect for smd soldering. I test at 20/20 but have something like reverse tunnel vision, so I see things just around center most clearly. Makes fine detail work kind of hard.

Conundrum

Sun Jan 17 2010, 11:07AM

Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4061

i ran into this issue too with the fc30 orientation sensors.

i solved it by using superglue to point hold the package "dead bug" style to a piece of veroboard, then solder small pieces of wire from a piece of electrical cord to the pads and pcb using 40 gauge solder.

solder was obtained from a very generous guy who runs a camcorder repair shop and had a reel left over.

its better to use a custom pcb and this same solder or just use solder paste.

as for doing really fine work, i was looking into using two kid's microscopes offset at an angle using Shapelock, with a video camera on each objective lens connected to my 3D goggles.
for this application you can use red LED illumination of the workpiece.

-A
"Bother" said Pooh, as his B/W print stopped for lack of magenta...

roddenberry

Sun Jan 17 2010, 09:25PM

Registered Member #2272 Joined: Wed Aug 05 2009, 01:34AM
Location:
Posts: 7

I second the suggestion of using solder paste, but I find that a very fine tipped soldering iron will do the job just fine, good solder flux is a must too, and can be used to dilute the solder paste a bit (when it's too thick).

Most SMDs are made expressly to withstand high heat for a short while (solder reflow process) but i'm pretty clumsy and my only experience with a toaster oven resulted into an unusable mess... ;)
- Robert

thedatastream

Mon Jan 18 2010, 10:27AM

Registered Member #505 Joined: Sun Nov 19 2006, 06:42PM
Location: Yorkshire!
Posts: 329

Tack each end of each edge down (8 points in total)
Drag solder slowly with LOTS OF FLUX (important)

Nicko

Mon Jan 18 2010, 12:34PM

Registered Member #1334 Joined: Tue Feb 19 2008, 04:37PM
Location: Nr. London, UK
Posts: 615

be very very careful of using solder paste with biggish SMDs and a hot air pencil - only use a fine tipped iron then solder wick to clean up.

I also use a USB microscope (fairly cheap on eBay) to visually inspect fine-pitched SMDs for bridges... some bridges are pretty much invisible to the naked eye...

Why not to use a hot-air pencil? - because it blows conductive paste under the chip which then causes invisible shorts, that's why

Dr. Who

Tue Jan 19 2010, 02:34PM

Registered Member #326 Joined: Sat Mar 18 2006, 01:12PM
Location: Glasgow, Scotland
Posts: 66

I use solder paste with a wide, flat soldering iron tip for SMDs. Scraping between the pins with the tip of a needle often gets rid of fine solder bridges.

Solder bridges are a problem with commercially-fabricated prototype boards, in my experience. With complex digital boards, I've found it helpful to run an acceptance test designed to detect short-circuits, using appropriate software and a logic analyser.

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