Cleaning PCB after soldering

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Cleaning PCB after soldering

Postby paselfc » Tue Jan 24, 2017 5:29 pm

I have a question about PCB cleaning.
Which is the best way to clean the PCB after soldering?
Is it good enough with IPA (isopropyl) or with the Flux Remover spray?
We use a lead free solder wire (3,5% flux inside the core) and after the soldering its a visible wetting,flux around the joint.When using the Flux remover the surface gets clean but it leaves sticky on it (when touch with fingers).
Same things occurs when cleaning with IPA.
The PCB material is FR4
Anyone with solution?
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Re: Cleaning PCB after soldering

Postby Ramon » Wed Jan 25, 2017 11:17 am

Hello Paselfc,

Depending of the flux type used cleaning with IPA of flux cleaner may be sufficient. In general, liquid fluxes are easier to clean when compared to gel fluxes.
Whether you can use brush + solvent on the assembly is determined by:
- Flux type (Internal or External in types: Gel or Liquid)
- Soldering application (hand or machine soldering)
- Physical properties of components (enough clearance for a brush to enter?)
- Location on the PCB of the area to be cleaned

To start: Internal flux is the flux inside the solder wire or the paste. So when soldering there's always flux applied.

Analyzing the situation: We need to start at the soldering application to determine which solder process is used. This to determine if cleaning is required. For hand soldering goes: In general a hand soldering process with external flux is never a no-clean process. The operator will apply the external (additional) flux manually and the dispensed amount will vary on every application. For a soldering process to be no-clean, it must be guaranteed all flux has been activated when soldering.
With machine soldering, the heat is applied to the whole pcb and flux qty's are more defined. So a machine soldering application will more easily apply to no-clean conditions.

Driven by your other question, it is assumed we're addressing a hand soldering operation. So you must clean flux remains when external flux is used.
Depending on the physical properties (size, pin spacing etc) it could be impossible to clean with solvent + brush (eg. fine-pitch multiconnectors). Would the area to be cleaned by more towards the center of the pcb, one would only spread the flux residue over the area, instead of cleaning).
Would the hand soldering process rely on the sole use of internal flux (flux-cored solder wire), then there is a fair chance the pcb could apply for no-clean. For that matter it is advised to perform cleanliness tests (eg. IPC-TM-650 § 2.3.27) to determine if a cleaning cycle is in fact required.

General conclusion:
Brush & solvent could be a viable cleaning method in repair operations. On rework or assembly process manual cleaning is not advised. An operator could forget the cleaning step in the process or be less thorough on cleaning. Advise to wash pcb's after hand soldering with external flux in the assembly process. On handsoldering with internal flux, perform tests to determine if cleaning is necessary. The advised cleaning cycle of new assemblies is a washing method (eg. ultrasonic). Manual cleaning (for new assemblies) with brush and solvent is not reliable enough to guarantee consistent performance.
Keep calm and focus on soldering
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Re: Cleaning PCB after soldering

Postby Anderson » Thu Mar 16, 2017 5:25 am

I have found some good tools for cleaning of PCB at However, I haven't purchase them yet but I think it might be good one. I also use Methanol (Methyl Hydrate) to avoid Lighter Fluid completely as it really useful for dissolving sticky residue.
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Re: Cleaning PCB after soldering

Postby totalmedtech » Thu Jul 19, 2018 8:57 pm

i use METHYL HYDRATE 99.9 pure,it`s around 10$ a galon(3.78 litre),or u can use isopropyl alcohol for delicate boards (it`s usualy safer) as for price is somewhat the same
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Re: Cleaning PCB after soldering

Postby DaveRodda » Wed Nov 14, 2018 6:41 pm

I sometimes use an old toothbrush on the boards to get into the nooks and crannys. We also do drop boards into a ultrasonic cleaner with IPA. There is a caveat to this. If you have any parts which are not to be washed, this is not a good idea. Usually these parts are buttons or dip switches. The Datasheet will say. Also there are possibilities you may break a chip with ultrasonic. Most of the time I do not have problems, but when I do it's typically a crystal which dies.

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