Advise for Difficult SMT soldering

By: ionn

2009-01-11 22:01:14

I saw a post on the Dorkbot PDX group in regards to using specialized components to make it easier to solder small SMT parts and keep them in place. I used a simple re-usable method some years ago using only microscope slide cover glass and a little extra solder flux paste.

Microscope slide cover glass comes and various thicknesses from 0.13 to 0.17 mm, and can easily be obtained.

You need to trim away some pieces of the glass and shape them into a size you're comfortable using. I suggest somewhere in the following range:

If you're a big fan of Sir Arthur C. Clark, you want them to be exact 2 x 3 mm parallelograms. That way they'll be full of stars... ;)

When you, or maybe someone more skilled than you, makes the glass tiles. Use them in the following manner:

Apply a copious amount of Flux Paste between pin 1 and 2 and then do the same between the two pins on the opposite side of the part. If it's an 8 pin SMT part, you'd place the second glob of paste between pin 7 and 8. Take a glass tile and stand it on end directly between the solder pads for pin 1 and 2, and with the second glass tile do the same on the other side. Whether you do this with the SMT part in place or not is up to you. The Flux Paste should be cool enough sot it keeps the glass tile standing upright since they're nice and light. With the SMT part in firmly pressed down in place and hugged by the glass tiles, solder the 2 pins farthest from the glass tiles. Remove the glass tiles and put them in place for the next part, not necessarily a multi-pin part as this works for any SMT part so long as you're not soldering too close to the Flux Paste holding the glass tiles as it may melt and the tiles may slip away. Keep the tiles stored in a nice clean safe container, I used a contact lens container that screwed closed for the Left and Right eye side separately. So long as the Flux Paste stayed clean, I left it on and placed them in the Left side as leaving the paste on kept them sticking to the side so they wouldn't move around. If the Flux was dirty I put them in the Right side with some Isopropyl rubbing alcohol I drained as needed and cleaned when I needed them.

>>>Making the Glass Tiles<<< Working with the thin glass to shape them can be a pain and may take a few failures (it's called learning!) before you get it right, but once you have the little tiles made, they come in handy.

You'll need the following:

Step 1: Tape off the area on the glass slide cover on both sides for the area you will be separating from he main part of the slide. Also tape on both sides the rest of the slide cover. Leave a small exposed area going from one end of the slide to the area where you will score the glass with the file or the glass cutter.

Step 2: Put on the safety glasses and get used to keeping them on for the rest of the process. If they're not comfortable and you may want to take them off, go get a pair that you can wear and forget you have on. You don't want tiny shards of glass in your eyes. The cost of a good pair of safety glasses is far less than an ER bill and the trouble having to deal with it. Paranoia is your friend, listen to it.

Step 3: Put the taped glass slide on a smooth, hard surface you (or whoever may own it) don't mind having it scratched by a file or glass cutter.

If you have a nice hard plastic cutting mat be sure it's not warped and sits very flat on a harder flat clear surface. If the cutting mat has become warped, put it on a cookie sheet (preferably with a piece of thick Real Wool between the cutting mat and the cookie sheet, and old scarf cut to size works nicely. If you're not sure it's wool, trim a piece off and try burning it with a match or lighter and see if it melts, and hold it in some tongs away from your face and fingers.)

Place the cookie sheet, wool & cutting mat into and oven pre-heated to 100 - 130 degrees Fahrenheit, keeping in mind you're doing this at your own risk. Heat them for about 5-8 minutes or until it's soft and is easily. Turn off the oven and take them out and immediately with pot holders in both hands place the cutting mat on the hard surface and cover with the wool and then a bunch of heavy books and let it cool there.

Step 4: Score the glass with the Glass Cutter or the small Metal File from one side of the glass to the other. Don't press too hard. Start by applying no pressure, and then gradually add small amounts of force over time. You may need to practice this and ruin a couple slides. You may consider doing many layers of the Masking Tape on both sides of the cutting area to create a good guide for your cutting tool.

Step 5: (Are you still wearing the Safety Glasses?) Snap the glass along the scored line.

Step 6: Once you have a long piece of glass a little bigger than the final width you want, use the razor blade to trim away an thin line of the tape where you want to score the height line. Score and snap the glass as per previous instructions.

Step 7: The exact method is up to you how you achieve it. Use the Small Metal File or Fine Grit Sandpaper to clean up the edges and make them as flat and perpendicular to the face of the glass tile as you can and file way the sharp corners so they're rounded. Don't worry about keeping it shiny and polished, you just need it functional.

Step 8: If your done making the tiles and are not about to start soldering, you can take of the Safety Glasses. Unless you're grabbing your Red Ranger BB-Gun and are about to go do something stupid.

Sorry, no pictures of this right now. I need to make a new set of tiles sometime soon (I've been moving a few times the last 5 years and lost that contact lens container) as I'm about to start working with SMT parts again. So maybe I'll post that as a movie on Vimeo.

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