memory slot solder reflowing temps

[gahbahj]

my front memory slot has stopped working so i've read all about reflowing the solder and looked at the google video. i have a solder station that goes from 0-850 that i picked up at an electronics surplus. i dont have a needle point tip - should i get one? where? what temp should i run at? will 2-3 seconds contact be sufficient or are there other physical ways to tell if the job is well done? thanks for your help.

[ZAGNUT]

i would say to get a fine chisel tip as this will have more contact area and heat the socket pins quicker. temp should be a bit higher than what it takes to quickly melt 1mm or so solder wire with the very end of a wetted tip....

get some flux in either a pen or bottle but make sure it's the good old fashioned rosin like kester 186, DO NOT use any of the so called no-clean or water soluble fluxes as they can be fiercely corrosive...

slather the pins and pads with the flux and then wet your iron with a tiny bit of solder and quickly touch the solder joint with the tip. you should see the flux boil off quickly and a tiny bit of solder get wicked into the joint. if you screw up and leave a big blob of solder on the joint or bridge a couple of pins then slop some more flux on and touch it with a clean tip. you shouldn't need to touch each pin for more than a second to get the job done.


some will say that you don't need to add any solder but there is plenty of room for a bit more and more importantly having a bit of solder on the tip gives you much better contact with the existing joint and helps heat it up much quicker.



dave

[poshgeordie]

I totally agree with Zagnut.

Liquid flux is the key to good resoldering, and you shouldn't need to add any more solder - in fact if you do that you may well get a solder bridge right up under the plastic of the memory slot.
Should that happen, apply more flux, get some desoldering braid, soak that in flux as well, and use a fine tipped soldering iron to melt it out.

The other important step is to make sure that the soldering iron bit is shiny silver clean. This compares with dull metal clean, which isn't actually clean at all but covered in a layer of old flux.
If the bit gets in that state heat is not transmitted through to the pins, and you can leave the tip on them all day without getting the solder to flow!
To clean the muck off, use a heavy duty tip cleaner such as those onthis page.
Alternatively wire wool works quite well but can leave tiny metal particles on the tip, so inspect the tip carefully before using it to solder the pins.

I've tried a number of different irons and tips, and the best one for me is a 25W iron with quite a big tip. It looks far too large for the job, but it solders 2 or 3 pins at a time and only needs to be applied for a couple of seconds a time.

Finally...! I've found that the pins that need soldering are mostly those at the ends of the pins groups; these are the pins at the actual ends of the assembly on both sides, but also at the end of the small group of pins and the beginning of the longer sections next to them.
I very rarely have to solder all the pins, only about half a dozen of them.

[ZAGNUT]

i agree that a big chisel tip on a low watt iron would also work great for doing a few pins at a time and you would not want to add any solder doing it this way.

those little tip cleaners are great but since i'm cheap i use the pot scrubbers from the supermarket. same exact thing but made from stainless steel instead of brass. these are harder on the tip's plating but then all my tips are bare copper anyways....

best way to clean a tip IMO is to thoroughly wet it with rosin core solder and then give it a good wiping.


dave

[poshgeordie]

best way to clean a tip IMO is to thoroughly wet it with rosin core solder and then give it a good wiping.
dave

Agreed too Dave - if the tip gets to the nasty grey state then it hasn't been cleaned for a while anyway! Doesn't say much for my tip housekeeping LOL

[gahbahj]

thanks for the info so far. i will try my flat tip to do 2-3 contacts at a time with some flux - "burnley non-corrosive soldering paste" - i will apply it with a needle. i have a copper braid for cleanup. the soldering station has a sponge in a dish which i have used to clean the tip on the wet sponge as i go, leaving a shiny tip. should i be concerned about some residue which isn't plain to the eye?

can someone please talk about temp range to use? i think i read somewhere to use ~600F for electronics soldering, which i have used in the past. thanks again

[poshgeordie]

Rather than using the paste you suggest, you need liquid flux like:

http://www.newark.com/00Z1870/tools/pro ... ics-cw8100

This is what is known as a no-clean flux where the residue can be left on the board after resoldering. No flux cleaning fluid is needed.

I believe the flux you're thinking of using is more for used in the plumbing trade.

Re the soldering iron temperature, 600 - 650F range should be OK

You shouldn't need desoldering braid for this, since you are just reheating the joints to reflow the existing solder so there shouldn't be any bridging.
When resoldering the pins, apply the flat part of the tip over the mem slot pins. almost immediately you will see the flux bubbling and smoking and the solder will melt.
At that point pull the soldering iron tip away from the mem slot body in a wiping motion.
The whole process should take less than 5 secs.
Don't apply too much pressure since you could damage the pcb track. The flux tends to prevent this by keeping the solder on the joint rather than flowing across to its neighbour.
If in the unlikely event you do get a bridge, apply some more flux and repeat by wiping away from the slot body.

[poshgeordie]

Double post

[ZAGNUT]

i do believe that burnley stuff is rosin based so it'll do fine. since it is in paste form get a small "0" or "00" sized paint brush to apply it with. you can use q-tips and alcohol (95% is best) to clean up the flux residue after soldering but do it quickly or the residue dries out and becomes a lot harder to clean.

if you haven't done this type of soldering before then find an old PCB to practice on. something like a motherboard or CD drive will have some fine pitched SMT parts. watch the flux you put down on the board and how it behaves when soldering. if it flows out, fumes a bit and is still a bit tacky after soldering AND your joint is nice and bright with smooth fillets between the pin and pad then you got the temp right. if the flux smokes violently and turns into a dark crusty substance then either your temp is too high or you're keeping the iron down for too long.

the soldering station has a sponge in a dish which i have used to clean the tip on the wet sponge as i go, leaving a shiny tip. should i be concerned about some residue which isn't plain to the eye?

that'll do just fine. the reason the "brass bundle of pubes" is considered better is because it doesn't thermally shock the tip and supposedly makes it last longer.



dave

[gahbahj]

thanks, all the questions i asked have been answered.
before i look for different flux, i will double check with u people on this burnley tin of flux ~ about the size of a chewing tobacco tin. it says it contains zinc chloride, but nothing about rosin or anything else except "harmful if swallowed." i have used it before soldering electronics with success. only burning stuff a couple times ;o)

[ZAGNUT]

zinc chloride is bad, bad, bad. use it for soldering pieces of metal together but not on electronics where the residue can hide under components.

the easiest to use will be a good RMA (rosin mildly activated) like the kester 186, preferably in liquid form. while some of the newer "no clean" types sound good they can actually be very corrosive if the residue they leave behind is disturbed and the water solubles are also bad unless you can get every bit of residue off which means washing the board in a bath.


dave

[gahbahj]

thanks zagnut and everyone else.. i'm off to find proper flux now :)

edit: i found kester formula 186 rma flux pens at local grainger store on clearance for $1.25 ea. - got a couple which will prolly last me a lifetime.. hehh