Desoldering

[yoyo1323]

Hi everyone,

I am trying to desolder a DC Jack and miscallaneous parts from and old laptop. The DC jack I really would like to desolder. I have a 25W Iron and a 30W Iron from raioshaq that I am using. However, it does not melt the solder. The part gets hot an a little bit of solder sticks to the desoldering braid but not any significant amount. I tried heating it without the braid and still it does not melt the solder. I tried solder that I have to solder parts and that melts just fine. Does anyone know what is going on? Do I need a solder Iron with more wattage?

Thank you!

[MonMotha]

The people who make laptop (and desktop) motherboards apparently don't know what a thermal relief is.  Those power connectors and other components on motherboards are soldered directly into giant power planes.  Basically, it's like trying to solder to (or desolder from) a giant heatsink.  Doesn't really matter how powerful your iron is (and no way 25/30W is enough), you simply can't dump heat into the joint fast enough to melt the solder.

What you need to do is basically bring that section of the board up to reflow temperature.  I just use a plain ol' heat gun for this.  Yes, like one would use to strip paint.  I have one of the fancy adjustable temp ones from Wagner Spray Tech, but a normal one will work.  Just use the "low" setting.  It'll get plenty hot.  Wave it around over that area of the board until it gets hot enough for the solder to be molten, then lift the jack off using needle nose pliers.  Be very careful when you do this.  It will take about a minute or so to get that section of the PCB hot enough, and then you need to act quickly.  You don't want to start a fire, and if you bump things around too much, you'll also cause parts to move around or fall off the board (remember, the whole area is molten).

If you'd rather not do this, then you can try using several reasonably high power, temperature controlled irons.  You'll need one on each section of the jack that's soldered down.  There's no way you'll be able to wick enough solder off of there to just remove the jack.  You have to get the whole thing to reflow at once.  I've never had much like with this method.  The only real method I've found that works is the heat gun.  The heat gun works pretty reliably, but you've got to get the hang of it, so try it out first one some scrap boards or similar (real FR-4, not that crap phenolic FR-2 crap they use in TVs and monitors).

[yoyo1323]

Thanks for the reply!! It helps out a lot.Im a little new at all this electronic stuff. Now I am wondering what kind of heat gun to get? I found a solder gun at Jameco rated at 100W is this enough? Is a solder gun the same as a heat gun? If I were to use an soldering Iron(cheaper $$) would 40W be enough or would it have to be higher?

[MonMotha]

A heat gun is like a hair dryer on steroids.  It moves a lot less air (volume) but the air it puts out is much, much hotter.  Do NOT attempt to dry your hair with it.

You can find them in hardware stores usually in the paint stripping area as that is a common application.

You can try using a large soldering gun, but I've found that I usually just end up burning the PCB as most are not temperature controlled, and the surface area of the solder joint limits the ability to transfer heat in which means that, no matter how much power your soldering tool is capable of producing, that joint will never fully flow.

[Ed_McCarron]

Those power connectors and other components on motherboards are soldered directly into giant power planes.  Basically, it's like trying to solder to (or desolder from) a giant heatsink.  Doesn't really matter how powerful your iron is (and no way 25/30W is enough), you simply can't dump heat into the joint fast enough to melt the solder.

Heh.  What he said.  I tried to replace some bad caps on a motherboard and it took a 200 watter to get even warm.

Never tried the heat gun.  Learn something new every day.

[Kevin Mullins]

A heat gun can be a wonderful addition to the soldering list of tools.... but practice using it on some junk boards first, can also ruin a board rather quickly too.

Sometimes when I need that little bit of extra heat I double up my iron with my desoldering iron, use both together.
http://www.radioshack.com/product/index.jsp?productId=2062731&CAWELAID=107592455
Allows you to suck some of the heavy solder off just as it gets hot enough to flow.

[MonMotha]

A heat gun can be a wonderful addition to the soldering list of tools.... but practice using it on some junk boards first, can also ruin a board rather quickly too.

I said it, too, but I'll reiterate it one more time.  It takes some practice to get the hang of using a heat gun on a PCB.  From the time leaded solder (god help you if it's lead free crap) flows until the time you'll start to delaminate standard FR-4 if you keep the heat on it is only about 15-20 seconds.  370HR will give you a little more headroom, but 370HR is usually only seen on lead-free boards where you NEED the extra headroom.  You have to keep an eye on what's going on, keep the heating even (feather the edges of the hot zone by moving the heat gun in a small, circular pattern), and act fast once things are at temp.  You can let it cool and try again about 5-10 times before the PCB starts to fall apart.

Do not attempt to use a heat gun on phenolic FR-2 type boards like seen in TVs and monitors.  They'll just fall apart and smolder (but they shouldn't hold a flame once heat is removed).

If the board has lead free solder, you can sometimes improve workability by flowing some leaded solder into the joint to make it a tin-lead or tin-lead-silver combination.  Often, I've found that I can get the joint to flow just enough to do this even if I have no hope of actually wicking any solder off of it.

[MB]

Sounds strange but it sometimes helps if you first add a little solder to the joint before desoldering.
It will help to transfer the heat.