How to Solder these

Hi,

I have some of the MAX7313AEG+ from maxim in the QSOP package ( below ).

https://www.electro-tech-online.com/custompdfs/2007/01/21-0055FPDF.pdf

MAN these things are small but iddy bitty legs! Does anyone have any recommendations on how to solder these blasted things?

Peter

Solder paste applied to the board with a sharp object, e.g. xacto knife, toothpick, then use an iron with a sharp tip. Don't worry if the paste smears to an adjacent pad/pin because as it heats it will be drawn to the pin. Do be careful of getting paste under the component as it may not heat and leave a puddle, causing a short.

My opinion is no solder paste. Just stick a bead of solder onto the tip of the iron, add flux to the pins in a row, and drag your soldering iron over them (just the solder bead! don't actually touch the tip of the iron to the pins and drag!) laying down a row of solder. Then check for bridges and remove with solder flux. (you can also just use suck all the solder off, which should leave the solder that got beneath the pins intact).

uhhh...remember to position and just tap the pins at opposite corners with the soldering iron to hold the IC in placebefore you do the dragging part.

I have not tried soldering smd ics yet, but when I eventually try it, I would go for the idea of soldering them as normal then removing excess with solder wick.
Looks like a temperature controlled soldering iron is useful.

Here are a few internet smd soldering guides:

https://www.sparkfun.com/commerce/present.php?p=SMD-HowTo-1

https://www.electro-tech-online.com/custompdfs/2007/01/Low20Cost20SMD20Soldering20Guide.pdf

I daily solder SMDs at work and tried all methods available. Solder paste is what produces the best results for me. No sucking, no wicks, no bridging, no mess. It would be easier if the syringe the paste came in actually had a needle on it, but it doesn't which is why the sharp instrument is needed. Sharp plastic tweezers are used to position the component.

I use the same station as shown on the sparkfun link picasm posted, set at about 680 to 700F. Anything cooler seems to take too long and damage to the IC is possible.

The solder bead method isn't a bad idea but I don't like applying solder that has been sitting and boiling on the tip. When solder is overheated you end up with peaks and bridges, and overheated solder is what you'll get if you let it sit and boil on the tip.

In the end, it's whatever works best for you.

If I'm not mistaken though solder paste has a few drawbacks for the hobbyist. It's expensive for how much you get, it requires refrigeration and it has a limited shelf life?
You do this stuff at work spiffitz, how true are the above statements? It's only what I've heard, but I'm asuming that someone in a production environment isn't going to have a problem with storage and shelf life because you use enough of it not to have to worry about it.
Flux paste is defintly a must have though, because even though solder paste works you could end up with solder bridges if you layed on too thick a layer. Simply reheating the solder is not a good idea the paste is a good rework tool.

The last tube we bought was purchased in August/September of 2006 and I just leave it on the table at room temperature. I work in a warehouse environment so the temperature reaches both extremes depending on the weather. The tube does need to be capped or it will dry out. When I need to use it I squirt a bit on a piece of paper and harvest it from there. After it sits for maybe 40 minutes I notice the carrier starts to evaporate and leaves mostly sticky stuff.

Shelf life problems I haven't encountered and I don't use all that much of it - it is mostly for SMD work. My daily chores consist of approximately 80% "normal" soldering and 20% SMD. Price could be of concern from a hobbyist standpoint, considering a 35gm syringe costs about $40USD.

The only bridging problems I get with solder paste is if the component isn't aligned too well and the paste can't decide which leg/pad to stick to. The goop is mostly carrier liquid so even though it looks like the application is sloppy as soon as it heats the carrier evaporates and solder flows to the leg being heated.

The method I use is a special soldering iron bit, with a little hollow in it, you load the bit with a 'blob' of solder - a professional version of what dknguyen suggested.

Brush the tracks with liquid solder, then carefully place the chip in place, then tag a couple of corners using a VERY fine soldering iron tip. Next brush over the pins with the liquid flux - finally draw the 'spoon bit' along the rows of pins.

This produces perfectly soldered chips, with no need for any solder removal afterwards.

The unit I use is a Pace SM Soldering station.

First I tin all the pins on the IC, then I solder one pin in the corner of the IC, get it aligned perfectly and solder each pin by placing the iron on it without using any aditional solder.

Nigel and dknugyen have the standard solution - sometimes the tip is called a "hoof" tip, but nearly anything will work. The critical thing is using enough flux - the sticky goop in solder paste is just a slightly tweaked flux, and if you plan on using applying solder from the tip (versus from the flux-cored solder off the spool), you'll need to have some flux on the part/pad itself.

Buy a flux pen - they're a couple bucks and they make life so much easier. The flux deoxidizes the solder and makes it flow properly.

Tinning pins on a small-pitch part isn't a great idea though. The part won't be flat, and you run the risk of non-soldered pins that are really hard to tell.

Incidentally about solder paste - I have had issues with flux leaking out the plunger end of the syringe, so there is definitely a limit to how long you can keep it around. I'd say over 6 months or so if you're pretty good about keeping it cold.