solder smd (two or more pins), some doubts...

[CharlotteSwiss]

Hello guys 
from the bottom of my inexperience I can quite well solder tht components.
I would like to improve the soldering of the smd components, but I have doubts about how to proceed with my equipment 
My work is not about new blank boards where to solder smd or IC, but only to replace smd or IC from faulty boards.
My equipment is:
- soldering station with 1.6mm flat tip and 0.8mm fine tip
- hot air station
- wich solder
-new purchase: flux chipquik smd291

I started doing some timid tests, but I have 3 doubts:

a) to unsolder smd or IC I use the hot air station, it is quite easy it seems to me; I have seen that in many videos they first put the flux on 
    the pins and then heat up to unsolder: is it necessary to use the flux to unsolder?

b) two pin smd soldering: I clean the pads with wich solder and then i clean with isopropyl alcohol, apply the flux on the two pads, put the 
    smd on, I put a drop of tin on the tip and go to solder the first pin (I hold the component still with the tweezers); then with a firm wire the
    second pin. Could it go as a procedure? I seem to perform the steps recommended in the flux instructions:
If soldering with wire solder:
 .Prior to soldering the SMD to board, pads need to be clean and level.
 .Apply flux on all Pads.
 .Place the SMD on pads, Use good lighting and magnification to ensure leads are centered on Pads
 .Carefully hold SMD in Place bY pressing down with pick or tweezers.
 .With a tinned iron, tack down 3 or more pins.
 .with a flat chisel tip iron (temp.controlled) apply solder as required and drag solder across all Pins
 .If a solder bridge is formed, use flux and solder braid to remove bridge.
 .Clean solder joints with isopropyl alcohol.
 .Inspect all solder joints for defects.

c) multi-pin smd soldering (IC): I'm confused here.
   I did not understand if it is better to clean all the pitches as described above, then apply the flux, and putting a drop of tin on the tip then 
   drag on all the pins.
   I have the doubt because the package together with the flux smd291 says:

  If reworking a surface mount board:
   .Apply CHIPQUiK flux and use soldering iron to reheat joints
   .Extra flux helps ensure solder will flow where needed and avoid short circuits
   .If desired, remove excess flux using isopropyl alcohol and lint free wipes or cotton swabs.

Since in the flux instructions, as I have reported above, they describe the procedure if you weld with wire, does this second procedure take place without using the wire? In practice they suggest to unsolder an IC for example, DO NOT CLEAN all pad, apply the flux and by heating the new IC will be welded (using the old tin still present?)

Any advice to solve my doubts?
thanks
 

[Jwillis]

I'm not an expert on SMD soldering . What I found was not to be cheap with the flux . Large multi pin IC's I find that if the pads are clean and as flat as possible things go better. Use solder wick to remove as much solder as you can apply flux to the pads  and proceed with tinned iron. Start in one corner and tack it down . Go to the opposite diagonal corner and do the same holding the chip down flat . Then do the other corners .
If you use plenty of flux then the solder flows really easy. To little and it oxidizes to much and won't work properly .I work the remaining pins outwards "painting"  the solder on a few pins at a time working in a crisscross fashion around the chip . If your shaky like me using some poylymide tape to hold the chip in place helps to keep it lined up to the pads.
I practised a little on some old dead boards de-soldering and re-soldering the components and found that this method worked the best from me.
If you have some populated boards your not using around to practice on then you can work out a method that works for you.

[CharlotteSwiss]

thanks jwillis 
yes of course I have various old cards in the cellar, I practice with those.
I've soldered some smd in the past (two pin only), not very well but it worked.
I asked why I now bought the flux chipquik smd291 and therefore I wanted some advice on how to use it best.
As I said above, if I look at the accompanying instructions, I understand the first part (wire welding), but I don't understand what they explain in the part "If reworking a surface mount board:", my English is very bad ...
If in the first part they explain welding using wire, maybe in this second part it is possible to use this flux without soldering with wire?

[tautech]

The iron you have will determine the tip choice that is best suited to your needs.
For SMD rework I use a station with both hot air and a Hakko style iron which for most use I use a chisel shape tip although many prefer a hoof style.
K/skew style tips are best for SMD rework as you can bridge both pads and either wipe the SMD passive off the pads of pick it off with tweezers.

https://www.hakko.com/english/tip_selection/series_900m.html
Hoof = BCM/CM
Chisel = D
Skew = K

I recommend getting a K style tip.

This thread is worthy of some study:
https://www.eevblog.com/forum/beginners/so-surface-mount-it-is/

[CharlotteSwiss]

thanks taut 

my soldering station is Ersa; I saw the video of Dave where he uses a blunt tip, and he puts the tin into the bevel and then drags; I don't have that kind of tip, but I think a chisel tip is enough (I have 1.6 and 3.2 mm).
I had already seen that topic, interesting.
I begin to think that the procedure indicated on the chipquik instructions "reworking .." is not the best, it is better to clean the pads first (so it will not be possible to solder the new chip simply by heating, but it will be necessary to put new tin)

[Terry Bites]

Go Flux!

[CharlotteSwiss]

thanks terry 
good moving
I understand that to solder smd integrated, the drag technique is fine when the pins are very close together; otherwise you can also solder pint to pin.
I miss that 45% blunt tip, I only have the tips of the image below.
Perhaps with these the dragging is not very easy ...

[CharlotteSwiss]

i saw the ersa video of their tips, the WD series is the ok one for dragging; but I can also try without that tip, I believe that many of you experts solder ICs with close pins without the concave tip
 

As an alternative to drag-and-drop work, I would like to try soldering a smd IC like this:
.I clean the pitches
.I put flux on the pitches
.add new tin on the pitches
.I position, and warm with the hot air station
.ic pins should solder
who knows if it works ... 

[rstofer]

It should work...

I don't use my hot air station very often because I don't remove large SMDs, I'm not doing repairs.

For SMD resistors and capacitors, I put some flux on the pad, tin the tip and, while holding the component in place with curved tweezers, solder the joint with the tinned tip.  The flux makes certain that the solder flows.

https://www.sparkfun.com/products/10602

Without tweezers, the parts walk all over the place.

For larger SMDs, I tack solder a couple of corner pins to get the alignment right, apply flux to the pins and drag solder.  I do have one of the club foot bits but I don't use it.  I just use an 1/8" chisel and it works fine.  Yes, I run out of solder before I reach the end of a row but that's not a big deal.  Just re-tin and continue.

Fine Solder Wick is helpful for removing any bridges.  i have a roll of 0.050" and a larger size just known as #2.  Both have their uses but for SMD, I tend to use the 0.050"

[CharlotteSwiss]

It should work...

I don't use my hot air station very often because I don't remove large SMDs, I'm not doing repairs.

For SMD resistors and capacitors, I put some flux on the pad, tin the tip and, while holding the component in place with curved tweezers, solder the joint with the tinned tip.  The flux makes certain that the solder flows.

https://www.sparkfun.com/products/10602

Without tweezers, the parts walk all over the place.

For larger SMDs, I tack solder a couple of corner pins to get the alignment right, apply flux to the pins and drag solder.  I do have one of the club foot bits but I don't use it.  I just use an 1/8" chisel and it works fine.  Yes, I run out of solder before I reach the end of a row but that's not a big deal.  Just re-tin and continue.

Fine Solder Wick is helpful for removing any bridges.  i have a roll of 0.050" and a larger size just known as #2.  Both have their uses but for SMD, I tend to use the 0.050"

hello rstofer it's a pleasure to hear from you 

For the procedure of soldering the hot cone chips that I described above, I will try it in the field.

Yes, I too for the classic two-pin smd, I do as you say (obviously I keep it with tweezers); I see a lot that first they put the solder on the pad, but I think maybe the method you described is even better.

For drag soldering, in fact you could do without the concave tip, in case you put it back on the tip again (I could use the 3.2mm one)

I saw that a problem could be the bridge between two adjacent pins, so with the desoldering braid it solves? Ok removes the pond from the bridge, but doesn't it also remove the pond from the pins / pitches?

thanks 

[rstofer]

For the procedure of soldering the hot cone chips that I described above, I will try it in the field.

Yes, I too for the classic two-pin smd, I do as you say (obviously I keep it with tweezers); I see a lot that first they put the solder on the pad, but I think maybe the method you described is even better.

I think tinning the pad is a mistake because it holds the component at an angle since we can only solder one pad at a time.  I want the component down flat against both pads.

For drag soldering, in fact you could do without the concave tip, in case you put it back on the tip again (I could use the 3.2mm one)

I saw that a problem could be the bridge between two adjacent pins, so with the desoldering braid it solves? Ok removes the pond from the bridge, but doesn't it also remove the pond from the pins / pitches?

Put some more flux around the pins that are bridged and lay some Solder Wick over the joint.  Heat to remove solder.  Again, the trick is to have enough flux.  Sometimes Solder Wick seems to dry out and whatever flux it was supposed to bring to the party is somehow insufficient.

Yes, Solder Wick will pull just about all of the solder out of a joint.  So, apply more flux and just tin the iron a little before reapplying solder.

It's not unusual to get bridges so having a plan to clean them up is useful.

[CharlotteSwiss]

Put some more flux around the pins that are bridged and lay some Solder Wick over the joint.  Heat to remove solder.  Again, the trick is to have enough flux.  Sometimes Solder Wick seems to dry out and whatever flux it was supposed to bring to the party is somehow insufficient.

Yes, Solder Wick will pull just about all of the solder out of a joint.  So, apply more flux and just tin the iron a little before reapplying solder.

It's not unusual to get bridges so having a plan to clean them up is useful.

ok I think I understand: if I had bridges between pins, I put flux in the bridge area and with the braid I remove the bridge (and adjacent welding by inertia ..). Then I put the flow back into that area, put a drop of tin on the tip again and go up; hoping that the bridge will not be created again, otherwise it will start all over again ..
I'll try the field as soon as I can
I could still take one of those concave points to place side by side with the two points I have. I see that they produce it with 1.6, 2.3 and 3.5 mm tip width, maybe the 2.3 one could be the right size (it doesn't matter if it touches more pins ..)
thanks rstofer
 

[Jwillis]

thanks jwillis 
yes of course I have various old cards in the cellar, I practice with those.
I've soldered some smd in the past (two pin only), not very well but it worked.
I asked why I now bought the flux chipquik smd291 and therefore I wanted some advice on how to use it best.
As I said above, if I look at the accompanying instructions, I understand the first part (wire welding), but I don't understand what they explain in the part "If reworking a surface mount board:", my English is very bad ...
If in the first part they explain welding using wire, maybe in  this second part it is possible to use this flux without soldering with wire?

I understand your question now.  In that case the chip is soldered but may have cracks or oxidation on the joints that may be causing the chip to not function properly. Basically all your doing is using the existing solder and reflowing the joints for better contact. By applying flux you don't cause extra oxidation when adding heat and any oxidation that is there can be removed with the flux. Kind of like dipping a tarnished penny into lemon juice . Since there is plenty of solder on the pins there is no need to add more.

[CharlotteSwiss]

I understand your question now.  In that case the chip is soldered but may have cracks or oxidation on the joints that may be causing the chip to not function properly. Basically all your doing is using the existing solder and reflowing the joints for better contact. By applying flux you don't cause extra oxidation when adding heat and any oxidation that is there can be removed with the flux. Kind of like dipping a tarnished penny into lemon juice . Since there is plenty of solder on the pins there is no need to add more.

thanks Jwillis.
I didn't understand what "reworking" was.
In practice, if a chip had any problems, it would be an attempt to recondition the existing solders; just put flux and heat, the existing tin melts and re-heated to the pins.
This could solve the problem.