What did I do wrong?

[orbiter]

Hi fellas,

First off.. Please don't laugh. Well ok then if you must

Right, I'm trying my hand for the very first time at reworking. I've got the necessary tools I need (I think.) And I can carry out general solder work pretty well.

To get me started I was having a practise on this old hard drive controller board, things were going very well. I'd managed to remove and replace some tiny resistors/capacitors ok, so I moved on to some DIP and SOIC chips, all went well. So my next attemp was with this PLCC chip, and as you can see it went horribly wrong It's not a problem becasue as I say I'm just having a go at this for practise.

My procedure was to heat the area in general with the gun, then move in closer and apply more heat around the joints until the chip came free. Once that was done my plan was to clean the solder pads of solder so that I could start again & re-solder the chip back in place, however this is where it went wrong.

I applied some liquid flux and went in with the copper braid and soldering iron. As you can see the top line of pads things went not too bad (for a noob,) however when I tried the bottom row the copper braid stuck to the pads a few times and made a right mess, even ripping out one of the adjacent pads.

What did I do wrong here guys? And could I have some pointers please for future reference as I'm going to keep trying this untill I can do it properly?




Thanks fellas

orb

[johnmx]

This is what I do in some special cases (using hot air):
1-   Apply hot air during 2min @ 150ºC
2-   Then 1min @ 180ºC
3-   Finally apply 350ºC to 380ºC just for a few seconds and the component should loose.
Well, more or less, it depends on each case. You get the idea. This is the only way to remove e.g. plastic connectors with tens of pins without melting the body.

[orbiter]

This was not during the hot air part or removal my friend, that part went fine. The problem was during the pad cleaning part where the copper braid was sticking to the pads as if it was welding itself. I was trying to keep the tip of the iron and the area clean, but it's as if the flux just overtook what I was doing and caused this gluey/soldery mess. Then I was having to add more solder to the tip to help remove the stuck copper braid from the pads.

orb

[johnmx]

Hum…in that case I think the problem was in the lack of temperature on the tip. If the tip is too narrow then you should increase (temporary) the iron temperature to something like 370ºC.
If you cannot adjust the iron temperature then I advise you to buy another solder iron with a larger tip and more powerful. A cheap one is enough for the job.

[Jimmy]

Try putting the flux on the copper brade you normaly puty the flux where you want the solder to go

[TheDirty]

The bottom part where your braid failed is because of the large ground plane that is shown in the picture in that area.  Your iron doesn't have enough power to heat soak that area.  It looks like all or most of those pins are part of the ground plane.

If you've tried the tips above, with flux and leaving the iron on longer and it still doesn't work, you're only option is to get a stronger iron.

[Mechatrommer]

do i have to laugh? this thing happened to me couple of time, i have enough laugh already. imagine the braid stuck to 2, 3 or more pad, you iron it and think it all melted where the truth only half of the pad melted, or usually all except one are melted. u think all of them are melted, so when you pull, u know what happen. since you used flux, try to minimized solder amount, not adding it more just like what u described, the trick is in the heat, as mentioned by others.

ps: low melt solder make wonder. pricey though. and i used side of the tip of the iron for this job, not tip of the tip

[williefleete]

agreed, that looks like a ground plane, and the iron didnt have enough thermal inertia hence the copper in the board and desoldering braid acted like a heatsink reducing the tip temperature enough to stop the solder from melting smoothly
try preheating the copper on the board with the hot air gun a little or increase the iron temperature
if the copper is cold the iron has to heat it up until the solder melts evenly

[orbiter]

Ah ok.. Thanks very much mates.

I do have various tips and a temp controlable iron but as you say the heat has probably been wicking away from the area really quickly via the ground plane, wick etc. Admitedly the tip I was using was only a 1.5mm chisel, although it was set to 380*C & layed sideways for better heat transfer, but obviously this was still not enough.  

Actually thinking about it, I could see the solder cooling almost immediately as I moved the iron around slightly on the solder wick, then the previous point would instantly stick to the work surface. So this clarifies what your saying.

Much appreciated fellas, I'll get some more practice in later on.

Regards

orb

[andyg]

Heres a tip you can use if you're having trouble heating up a joint due to a large ground plane. Sometimes, even the most powerful and expensive soldering irons still can't fight against a large planes thermal mass. Especially boards with poor or no use of thermal reliefs around the pad.

Preheat/soak the board in a oven, say at 130-160 degC until the whole boards gets to temperature. Take it out and then do the work quickly. It'll be a lot easier.

You'll need to check the other components on the board can handle the preheat. e.g plastic connectors etc.

[orbiter]

Yes good idea andy, thanks. I guess I could use the heat gun in this way too, by heating the work area up using the large nozzle and then going in with the iron.

Cheers

orb

[Psi]

yeah, it's amazing just how much better it is soldering with a fat chisel tip compared to even a medium pointed tip.

I find i use my big fat chisel tip more often than my regular sized pointed tip, definitly get one if you dont have one already.

[orbiter]

Got a couple more of the larger sized tips on order

Cheers

orb

[osmosis321]

The only good point I haven't seen mentioned so far is that you may have erred in attempting to remove that solder in the first place.

I usually just leave it on there; it protects the copper and if I want to replace the part, wouldn't you know it, the right amount of solder is already there.. all I need to do is flux it and it's ready for action.

[orbiter]

The only good point I haven't seen mentioned so far is that you may have erred in attempting to remove that solder in the first place.

I usually just leave it on there; it protects the copper and if I want to replace the part, wouldn't you know it, the right amount of solder is already there.. all I need to do is flux it and it's ready for action.

Agreed. That was an obvious really as I did notice that the solder was there on the pads once the chip was removed, and looking back it would have been the easiest thing to do. However I was really only having a go at practicing so wanted to try a total strip down and replace.

Thanks for the good tip though

orb

[alm]

The only good point I haven't seen mentioned so far is that you may have erred in attempting to remove that solder in the first place.

I usually just leave it on there; it protects the copper and if I want to replace the part, wouldn't you know it, the right amount of solder is already there.. all I need to do is flux it and it's ready for action.

Note that this is only true if you use hot air, since it allows you to melt the tin on all the pads at the same time. With a regular soldering iron, you would be unable to level the chip properly without removing the solder, which is why you usually start with tinning just one pad.

[orbiter]

Understood alm, thanks.

orb

[Alex]

Pardon me if I repeat what you guys have already suggested. I have read post 1 and 15.

The bottom row seems to be mainly connected to a large copper pour, possibly a ground plane. A lot more thermal energy need to be transferred to fully melt these joines, its like soldering a heatsink! You need to use an 'angled-face' tip with a diameter close to the pad height.

The adjacent pad should have not been damaged, probably the area got very warm and you touched that pad with the solder wick but the solder was not fully melt. Use a solder generously fluxed wick a bit narrower than the pad height.

If you must, place the board on a preheating plate (proper IR, hot air, sauce pan) at 100 deg C or so. A lot less energy will be required then to melt the solder.

To repair the pad see these excellent IPC-based videos:

https://www.youtube.com/user/SolderingGeek?blend=2&ob=1#p/u/8/meulzHIq4Us
https://www.youtube.com/user/SolderingGeek?blend=2&ob=1#p/u/9/dwrnWasLYUc
https://www.youtube.com/user/SolderingGeek?blend=2&ob=1#p/u/7/TFcPxCN93nY