Author Topic: Would solder paste or alcohol/IPA go inside an IC when soldering and cleaning?  (Read 517 times)

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Offline bjdhjy888

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For example, in this video, solder paste was used to tin pins. Then alcohol or acetone was used to clean up.
You can see the liquid form of these materials both covered the casing of the IC.
When I solder, the same thing would happen. I sometimes rinse my entire IC with 95% alcohol or IPA to clean it up.
So, my concern is, would solder past or acetone or IPA go inside an IC when soldering and cleaning? If yes, would they damage the internal circuits? Or, the casing of the IC is always very tight and nothing could go inside?
Please help. Thanks!



« Last Edit: August 16, 2019, 09:55:12 pm by bjdhjy888 »
 
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Offline T3sl4co1l

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The case is sealed, using a fairly rigid material.

If it cracks, environmental contamination can be exposed to the die, but more importantly, a bondwire (trapped in the encapsulant) has probably been broken in the process, and now the part is useless.

This is unusual to happen, even with soldering heat; but some conditions can cause problems.  For example, if the material tends to absorb moisture, which is then released rapidly at high temperature, it can crack apart.  Slow heating, and preferably a bake-out cycle (modest heating for a longer time, in a dry atmosphere), avoids this.

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Offline Kasper

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I think a more real concern is flux residue being left under the IC causing mild conductivity between pins or corrosion.

Not something that has come up much for me except in avionics when we had to hipot test. There was specific part that we would have to replace sometimes and if we didnt clean the board before and after installing the new one then it would fail hipot.

hipot test: apply high potential (~1000V) and make sure no current flows.
 

Offline RoGeorge

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...
So, my concern is, would solder past or alcohol go inside an IC when soldering and cleaning? If yes, would they damage the internal circuits? Or, the casing of the IC is always very tight and nothing could go inside?

No.  Yes.  Yes.

Offline chemelec

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NO.
And Alcohol will probably Not Remove solder Flux very good.
Acetone is better, than followed with some Water.

I Use Water Based Solder Flux, so just washing it off in Warm Water Removes all the Flux.
Personally I Recommend a Kester 331, .80mm Diameter, 63/37 Solder.
 

Offline tooki

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NO.
And Alcohol will probably Not Remove solder Flux very good.
Alcohol removes rosin fluxes just fine, though not as well as proper flux removers. Countless people use IPA to remove flux residues.

Acetone is better, than followed with some Water.
Acetone works well, but can be harsher on plastics, so can damage some components.


I Use Water Based Solder Flux, so just washing it off in Warm Water Removes all the Flux.
Personally I Recommend a Kester 331, .80mm Diameter, 63/37 Solder.
Very bad advice for the hobbyist. Water soluble fluxes must only be used in carefully controlled processes, in terms of component selection and in soldering and cleaning processes. They absolutely must not be used with stranded wire or with components where flux or wash water can wick inside. And they must be cleaned perfectly, every time, because even small amounts of residue will cause corrosion with time. Consensus is that water soluble fluxes are unsuited to hobbyist use.
 
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Offline Kasper

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NO.
And Alcohol will probably Not Remove solder Flux very good.
Alcohol removes rosin fluxes just fine, though not as well as proper flux removers. Countless people use IPA to remove flux residues.

All I use at home is IPA.  I think some people struggle with this because they don't remove the flux after the alcohol liquefies it.  Applying alcohol liquefies the flux but if left alone, the alcohol will evaporate and the flux will remain.  The trick is to remove the alcohol / flux solution after the flux has been liquefied and before the alcohol evaporates.  Kimtech delicate task wipes are great for that.
 

Offline floobydust

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Alcohol and water are not a long-term problem as they evaporate.
Had production problems with DIP-packaged IC's failing. TI changed the package years ago, and the cause of failures was flux ingress corroding the bonding wires and edges of the die.

Whether TI getting cheap with their packaging, production using aggressive flux in wave soldering, not sure but YES plastic packaged IC's are not totally sealed. Flux can cause corrosion damage. I'm not sure which fluxes are worst.
 
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Offline tooki

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NO.
And Alcohol will probably Not Remove solder Flux very good.
Alcohol removes rosin fluxes just fine, though not as well as proper flux removers. Countless people use IPA to remove flux residues.

All I use at home is IPA.  I think some people struggle with this because they don't remove the flux after the alcohol liquefies it.  Applying alcohol liquefies the flux but if left alone, the alcohol will evaporate and the flux will remain.  The trick is to remove the alcohol / flux solution after the flux has been liquefied and before the alcohol evaporates.  Kimtech delicate task wipes are great for that.
Yup!!

I've never understood why people think that using a solvent to dissolve debris is enough. Whether it's rosin flux on a PCB or dirt on the floor, just getting the contaminant dissolved/suspended in liquid isn't going to actually remove the contaminant, it merely spreads it around! I understood this even as a kid, and so it eludes me why people struggle with this concept.
 

Offline MosherIV

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Hi.

Getting back to the questions ask by the op.

Here is a link with a nice diagram of the different parts of a microchip
https://electronics.stackexchange.com/questions/28840/what-is-the-protective-layer-around-microchips-made-out-of/28845
There is little difference between the leg frame, whether it is DIL or QFP, j-lead etc when molding the packaging.
It confirms what I remember, that the black plastic material is some kind of epoxy resign.
It fully covers the entire silicone chip and the leg frame, only leaving the legs pertruding for soldering.
The epoxy is non porous, so liquids like IPA do not effect it.

I remember a colleague telling me that the change to RoHS meant that the epoxy used had to be re-formulated and the main difficulty was resistance to heat, ie survive soldering.
 

Offline bjdhjy888

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Hi.

Getting back to the questions ask by the op.

Here is a link with a nice diagram of the different parts of a microchip
https://electronics.stackexchange.com/questions/28840/what-is-the-protective-layer-around-microchips-made-out-of/28845
There is little difference between the leg frame, whether it is DIL or QFP, j-lead etc when molding the packaging.
It confirms what I remember, that the black plastic material is some kind of epoxy resign.
It fully covers the entire silicone chip and the leg frame, only leaving the legs pertruding for soldering.
The epoxy is non porous, so liquids like IPA do not effect it.

I remember a colleague telling me that the change to RoHS meant that the epoxy used had to be re-formulated and the main difficulty was resistance to heat, ie survive soldering.
Thank you for your explanation.
That said, just because an IC's casing is of epoxy and being non-porous does not mean the casing is water-proof or of IP67.
So, I would still be concerned if liquid would leak inside an IC during soldering, causing damages. Am I correct?
 

Offline bjdhjy888

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Speaking of alcohol v.s. IPA, I did an experiment for cleaning up, after I soldered my LQFT-48 chips last night.
The result showed IPA was way more powerful, when it comes to removing leftover solder paste.
Below you can see solder paste was still visial and hidden under the pins, whereas it's clean after using IPA.
My question is, should I use IPA and quit using alcohol? IPA is bad for my health?
Or, should I continue to use alcohol which is not harmful for my health, and I start to brush harder when cleaning my PCB?


« Last Edit: August 16, 2019, 10:05:29 pm by bjdhjy888 »
 

Offline T3sl4co1l

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Isopropyl alcohol is almost as low toxicity as ethanol is.  Side-effects aren't as pleasant, of course...

Acetone is essentially the same toxicity as well, because isopropanol is oxidized to acetone in the liver.

MEK is also quite effective, though again it's more aggressive against a lot of plastics, inks and so on, so needs to be used even more cautiously.  Avoid aliphatic (heptane, petroleum ether... gasoline?) and aromatic (toluene, etc.) solvents, they're very likely to damage things.

Don't poo-poo the commercial flux cleaners.  They're more expensive than solvents, because they work damn well.  A few spritzes, a little scrubbing or sonicating, another spritz to clean it off and you're done.  Huge labor savings.

Tim
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Electronic design, from concept to prototype.
Bringing a project to life?  Send me a message!
 

Offline MosherIV

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Quote
That said, just because an IC's casing is of epoxy and being non-porous does not mean the casing is water-proof or of IP67.
So, I would still be concerned if liquid would leak inside an IC during soldering, causing damages.
No, fully encapsulating the silicone with a non porous material is suppose to make it liquid proof.

The point of encasing the silicone chip is to a) protect the silicone chip, b) protect the bonding wires both mechanically and from contamination including liquids.

The encapsulation has been designed to survive circuit  board manufacturing. This means that the whole device has to survive reflow soldering : sitting on solder paste and going through infra-red oven for 20 minutes reaching temps of upto 250°C and finally being washed with commercial flux cleaner

Quote
Am I correct?
No!
 


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