Personal computing discussed

Moderator: JustAnEngineer

 
larry109
Gerbil In Training
Topic Author
Posts: 3
Joined: Fri Oct 13, 2017 1:56 pm

Soldering questions

Fri Oct 13, 2017 2:07 pm

I'm super new to soldering. I just want to get the basics down at first. I picked up a temp-controlled hot air gun and iron station, some wick, lead, flux, desoldering pump, tweezers, etc... I got a few junk modems laying around so i decided to test out and try to desolder the chips.

Looks like a bunch of 8-pin EEPROM chips on them. I added some flux to the legs, set the temp to 350 celcius on the hot air gun, circled around the chip for about 5-10 seconds and the chip easily slid off. But on a different modem, I could not get the EEPROM chip off for the life of me. Had the hot air going for 3-5 minutes, even raised the temp to 400 and it just wouldn't budge.

Is there some sort of special solder on this modem that makes it nearly impossible to get the chip off? Is there a better technique?
 
ludi
Darth Gerbil
Posts: 7452
Joined: Fri Jun 21, 2002 10:47 pm
Location: Sunny Colorado front range

Re: Soldering questions

Fri Oct 13, 2017 4:32 pm

Sometimes you have ground planes in the PCB that also act as fairly good heatsinks. In those cases you may need to desolder the pins individually using a cranked-up iron and either a desolering bulb or a reel of desoldering braid.
Abacus Model 2.5 | Quad-Row FX with 256 Cherry Red Slider Beads | Applewood Frame | Water Cooling by Brita Filtration
 
just brew it!
Gold subscriber
Administrator
Posts: 49743
Joined: Tue Aug 20, 2002 10:51 pm
Location: Somewhere, having a beer

Re: Soldering questions

Fri Oct 13, 2017 4:48 pm

Yes, ground/power planes can be a bitch. They act like heat sinks and keep the solder from melting. I learned that the hard way a while back trying to replace capacitors on a motherboard.

As ludi says, you may need to desolder the leads individually by hand.

Depending on when the device was manufactured, it may also be using lead-free solder. Lead free solder has a higher melting point (but I still would've expected 400C to be more than enough).
Nostalgia isn't what it used to be.
 
larry109
Gerbil In Training
Topic Author
Posts: 3
Joined: Fri Oct 13, 2017 1:56 pm

Re: Soldering questions

Fri Oct 13, 2017 4:53 pm

ludi wrote:
Sometimes you have ground planes in the PCB that also act as fairly good heatsinks. In those cases you may need to desolder the pins individually using a cranked-up iron and either a desolering bulb or a reel of desoldering braid.


Interesting....will this also save the chip from damage? Once I get some experience under my belt, I'm going to be diving into reprogramming EEPROMS and resoldering them back on.
 
larry109
Gerbil In Training
Topic Author
Posts: 3
Joined: Fri Oct 13, 2017 1:56 pm

Re: Soldering questions

Fri Oct 13, 2017 4:55 pm

just brew it! wrote:
Yes, ground/power planes can be a bitch. They act like heat sinks and keep the solder from melting. I learned that the hard way a while back trying to replace capacitors on a motherboard.

As ludi says, you may need to desolder the leads individually by hand.

Depending on when the device was manufactured, it may also be using lead-free solder. Lead free solder has a higher melting point (but I still would've expected 400C to be more than enough).


So I guess it's possible that 400C is not enough with a straight up hot air gun trying to remove a chip that has a ground plane? Crazy stuff. And the only way to find out if the chip has a ground plane is if it's not coming off the board quickly?
 
Chairman_Now
Gerbil In Training
Posts: 1
Joined: Tue Jul 03, 2007 2:21 pm

Re: Soldering questions

Fri Oct 13, 2017 5:35 pm

FYI, components are sometimes glued to the board - it's called "staking". If that's the case, no amount of heat is going to get it to budge. This was probably more common on older stuff, but it's possible that's what you're seeing.

If it's a power/ground plane, you'd need an underboard pre-heater, ideally, or you'd need to heat the entire component fairly quickly to get it off.
 
just brew it!
Gold subscriber
Administrator
Posts: 49743
Joined: Tue Aug 20, 2002 10:51 pm
Location: Somewhere, having a beer

Re: Soldering questions

Fri Oct 13, 2017 10:35 pm

Chairman_Now wrote:
If it's a power/ground plane, you'd need an underboard pre-heater, ideally, or you'd need to heat the entire component fairly quickly to get it off.

Or identify the pin(s) which are connected to the power/ground planes, and desolder those using a soldering iron with solder wick and/or a solder sucker tool.
Nostalgia isn't what it used to be.

Who is online

Users browsing this forum: Bing [Bot] and 1 guest