Soldering flux for solder paste

[Amalinda]

Im going to use MCN-300 Soldering Solder Paste 63/37 25-45um solder paste to solder an IC. can someone please tell me if mixing solder flux would be necessary? Would I be able to solder the IC with no flux? or is flux mandatory?

answers so much appreciated.

 

[tpetar]

It depends from many things.

Soldering expirience. Its possible to solder without soldering flux if you have expirience, and soldering place is relative clean from oxidation and clean in general. Soldering material should be added directly on soldering place. Also you need to have good soldering station with temperature regulation and good soldering iron tip.

You didnt specify which IC case. For TQFP and higher I will suggest usage of soldering flux.




Best regards,
Peter

 

[Amalinda]

Sorry about not mentioning the IC. its texas Instruments BQ25504. **broken link removed**is the link for the package.

Its my first time soldering, but im gonna practise a lot before I do this one. plus I will be guided by a person (a colleague of mine @uni) who has already done this sort of soldering.

Could you kindly recommend to me a paste that I should mix with my solder paste? and tell me how much I should mix it. ( e.g. 30% ?)

I was thinking of buying **broken link removed** as my solder flux and mixing it 30% with the solder paste. please let me know if I am wrong and tell me the correct way.

thank you so much

- - - Updated - - -

p.sp I have a very good soldering station provided by the university.

 

[tpetar]

QFN case I usually solder with SMD hot air rework station, final result is like factory solder. Anyway I will suggest usage of soldering flux with this case. First add soldering flux on soldering place/contacts, then add thin layer of soldering material on all pins and in middle area. Then again add soldering flux, add QFN IC over that, and use hot air station.

Also there is way to solder QFN with PCB hole in centre of QFN place, but I personally dont like this method.

Additional there is special soldering paste, which is used with hot air soldering station, oven or IR spot soldering.. This is easiest way. But that special soldering paste is expensive and have lifetime around 6 month after production. I use this a lots, and this is really easiest way.

How to Solder QFN MLF chips

About fluxes...

Fluxes for soft solder are currently available in three basic formulations:

Water-soluble fluxes - higher activity fluxes designed to be removed with water after soldering (no VOCs required for removal).
No-clean fluxes - mild enough to not "require" removal due to their non-conductive and non-corrosive residue.[5] These fluxes are called "no-clean" because the residue left after the solder operation is non-conductive and won't cause electrical shorts; nevertheless they leave a plainly visible white residue that resembles diluted bird-droppings. No-clean flux residue is acceptable on all 3 classes of PCBs as defined by IPC-610 provided it does not inhibit visual inspection, access to test points, or have a wet, tacky or excessive residue that may spread onto other areas. Connector mating surfaces must also be free of flux residue. Finger prints in no clean.
Traditional rosin fluxes - available in non-activated (R), mildly activated (RMA) and activated (RA) formulations. RA and RMA fluxes contain rosin combined with an activating agent, typically an acid, which increases the wettability of metals to which it is applied by removing existing oxides. The residue resulting from the use of RA flux is corrosive and must be cleaned. RMA flux is formulated to result in a residue which is not significantly corrosive, with cleaning being preferred but optional.

Flux performance needs to be carefully evaluated, a very mild 'no-clean' flux might be perfectly acceptable for production equipment, but not give adequate performance for a poorly controlled hand-soldering operation.

https://en.wikipedia.org/wiki/Soldering



I currently use MultiCore MF220. :roll:



Best regards,
Peter

 

[marce]

You cannot solder without a flux, (it may be possible but is nigh on impossible to get a good joint).
There is no such thing as a no clean flux.
You can get solder pastes with the flux already added, I would suggest this may be a better option.
The solder paste mentioned is non RoHS compatible, I presume this is for a DIY job and not commercial.