Why won't my solder behave?!!?

[DigiTan]

I hate working with surface-mount parts. It's impossible to control where my solder will collect even if I apply surface cleaner and flux. Here's a common scenario:

1. I want to solder an 8-pin IC
2. The first 7 pins finish smoothly
3. On the last pin, the solder jumps away and forms a blob across its neightboor pin. Or it sticks to the iron and turns an ugly charred color.
4. I try to correct the error, forming another short as I try to re-solder
5. Step 4 repeats for several minutes or even hours; turning a simple task into all-out battle. :x

What the heck is going on?!!? And why does my solder have a mind of it's own now? The main trouble I'm having is with all the damned surface tension, where it will stick to the iron like a magnet and refuse to return to the board. Also it likes to short across closely-spaced pins, and that's ruined many of my SOIC packages. It's so frustraiting, I can only stand to do 1 SMT project every year. :x

I'm already trying alcohol and flux.

 

[D.J.]

Hi,

The only reson, I can see, why the solder does not stick in a certain spot is becuase that area hasn't been cleaned enough.

"where it will stick to the iron like a magnet and refuse to return to the board"

Ya I get that sometimes. Solder is attracted to heat(soldering iron), so (if you haven't already) hold the soldering iron at the end of the pin, or far enough away from the soldering area, but still have enough heat to melt.

Is your boards held level? Do you use a scratchy pad to clean the board?

Hope this helps,

D.J.

 

[Morgen]

Put a small blob of solder on the pad before placing the chip. Then touch the tip of the iron to the solder and let the pin sink into the solder.

 

[Styx]

get some flux
also you might want to clean the pads with a bit of solvant

 

[DirtyLude]

Tin the pads before you start trying to solder the part.

Heat the pad and pin enough before applying the solder.

If you have an adjustable iron, try varying the heat.

In the end, it's easy to just do a messy job than clean everything up afterwards with solder wick and flux.

 

[bmcculla]

In the end, it's easy to just do a messy job than clean everything up afterwards with solder wick and flux.

Solder wick is really helpful for surface mount parts. Its great for separating bridges on fine pitch parts.

It also helps to heat the pad with the iron and touch the solder to the pad. The solder will flow up onto the pin much more reliably.

Get some really thin solder too. I use .020 for my surface mount stuff.

 

[instruite]

The best way to solder surface mount device is to apply solder on the pads then just keep the IC on the pads and touch the solder iron (without any solder on it) on the pins and slightly press them to the pad and your pin with get soldered to pad
I do soldering of TSSOP packages in this way and I dont even use flux and still all my circuits work

 

[mstechca]

Old solder tends to create shorts. Your best bet is to use lots of new solder. New solder has flux in it which keeps the connections perfect. Eventually, this flux becomes ineffective, and all you have is "metal paste".

 

[Russlk]

instruite said it best, except I use lots of flux and clean the board after.

 

[pandaemonium]

For surface mounts, I solder the foil and let the solder flow to the pin. If a couple of pins get bridged with solder, I heat the solder bridge and use a weak solder-pult to remove it. Since I let the solder flow to the pins there is still solder beneath the pin giving a good connection.

 

[Oznog]

Using SMD solder paste and an oven+heat gun is the way I do it, and it works great.

I had some problems with bridging and I found touching the bridged pads with the soldering iron and quickly dragging a fine wire or piece of component lead between the pins will separate the pads.

As long as you don't have solid copper on the backside, always shine a bright light from the backside and let it shine through the board. Any bridges will be clear if present.

 

[lavenatti]

Are you wiping the tip of your iron off? You could be accumulating enough crap on the end of your iron by the eighth joint to mess it up.

 

[evandude]

if I'm soldering any rather fine-pitch SMD IC's... I always just load all the pins with solder (one big solder bridge) and then heat it up and use a solder sucker to take off all the excess. works great.

 

[mstechca]

Be careful with the flux. If you use way too much of it, you might damage some parts.

 

[DigiTan]

evendude, that sounds exactly like what I need to try. Actually, this is what happened a lot of times by accident while I was applying many re-corrections.

What chemicals should I use for heating the soldering tip? Should it be cleaned hot or cold?

 

[pike]

I have tried the method suggested by evandude, it worked until I did some small ceramic capacitors and resistors (smd of course) and it sucked up the whole component with the excess solder!!

Just use solder wick, much more reliable.

 

[Roboticinfo]

reply

I would agree but I use the toaster oven method and it works great.

 

[mstechca]

toaster oven?????????

my god, that is worth more than audioguru's "BYE" remark. That is RIDICULOUS!

Why use a toaster oven? You will damage almost everything in your circuit!!!!!!!

 

[Roboticinfo]

reply

It is not what you think

I will explain the proccess later
because I don't feel like typing that long.

 

[Nigel Goodwin]

toaster oven?????????

my god, that is worth more than audioguru's "BYE" remark. That is RIDICULOUS!

Why use a toaster oven? You will damage almost everything in your circuit!!!!!!!

You're showing your inexperience! - although I've never done it, nor had any wish to!, it's a commonplace technique for SM soldering.

Perhaps you're not aware of how commercial PCB's are made? - the SM components are glued on the board, then the board is flow soldered by floating it over a solderbath with waves travelling down it. The SM components are designed to take a lot of heat!.