electroless, immersion, HASL

[metebalci]

Just out of curiosity, similar to ENIG, can HASL be called electroless solder immersion ? or the electroless and immersion in ISn and ENIG means something more/particular/else ?

[aeg]

HASL does not involve electroless deposition, so no.

[metebalci]

OK I see. I got the point but I realized I dont know the difference between soldering and plating at chemical level (however not sure if I can understand it with just slightly more than high school level chemistry knowledge).

[ebastler]

ENIG is a two-step process (first nickel plating, then gold on top), where both steps involve chemical reactions. A metal salt is provided and, via a reduction reaction, metal is caused to precipitate from that.

In contrast, HASL is a physical process only. There is no chemical reaction, i.e. no change of molecular omposition by breaking or creating bonds, but just a phase transition: Solder melts and hardens as its temperature is changed.

[jpanhalt]

Just out of curiosity, similar to ENIG, can HASL be called electroless solder immersion ? or the electroless and immersion in ISn and ENIG means something more/particular/else ?

Can painting a house be considered electroless deposition?  Yes.  Get real. Think of the intent.

[metebalci]

ENIG is a two-step process (first nickel plating, then gold on top), where both steps involve chemical reactions. A metal salt is provided and, via a reduction reaction, metal is caused to precipitate from that.

In contrast, HASL is a physical process only. There is no chemical reaction, i.e. no change of molecular composition by breaking or creating bonds, but just a phase transition: Solder melts and hardens as its temperature is changed.

Thanks, this was, particularly the second paragraph about bonds and phase transition, the answer I was looking for.

[metebalci]

Just out of curiosity, similar to ENIG, can HASL be called electroless solder immersion ? or the electroless and immersion in ISn and ENIG means something more/particular/else ?

Can painting a house be considered electroless deposition?  Yes.  Get real. Think of the intent.

I dont think it (naming) is related to the intent, it is related to chemistry. By the answer above, and again dont know about painting but I dont think painting a house can be called electroless deposition.

[Berni]

The point of electroless for ENIG is to differentiate it from classical gold plating where electroplating is used to drive the gold atoms onto the surface.

The problem with that is that you need an electrical connection to the thing you are plating for this to work. However once you have a etched PCB the traces are not all connected together anymore (that's the point of a PCB) so you can't use electroplating to plate the pads. So to get gold onto there you need ENIG where the gold is chemically driven to plate onto the metal pads.

HASL is just throwing the entire board into a vat of molten solder, pulling it out and then using compressed air to blow off any left over solder. Technically it is electroless, but there is no electroplating version of it so there is no point in mentioning it. Yes you can electroplate tin, but the chemical ways are so easy that pretty much only those are used.

But if we can ENIG gold onto there, why do we still use the shitty caveman electroplating way where we need a connection? Well ENIG makes a pretty shit coating. It is enough to prevent oxidation, but is not smooth or long lasting. So for things like connectors where the gold plating has to stand up to friction of contacts, there you need something better. So those are still electroplated. PCB manufacturers tend to call this "hard gold" where all the pins on the connector are temporarily shorted together for plating, then the shorted area is milled away afterwards. Giving you a high quality durable gold finish.

[metebalci]

The problem with that is that you need an electrical connection to the thing you are plating for this to work. However once you have a etched PCB the traces are not all connected together anymore (that's the point of a PCB) so you can't use electroplating to plate the pads. So to get gold onto there you need ENIG where the gold is chemically driven to plate onto the metal pads.

Very good point 

HASL is just throwing the entire board into a vat of molten solder, pulling it out and then using compressed air to blow off any left over solder. Technically it is electroless, but there is no electroplating version of it so there is no point in mentioning it. Yes you can electroplate tin, but the chemical ways are so easy that pretty much only those are used.

I think the term plating is important here, so either using electrical energy or not, this is the basic (chemical) process (ENIG or other type plating) and it differentiates it from soldering or HASL. So @ebastler 's reply makes sense to me. I dont know more chemistry than this to say a counter argument. Again from his reply, I take it as plating involves a chemical change whereas the process in soldering/HASL is just (or mainly) a phase change (forming an alloy with the metals I believe). I was not 100% sure if HASL/soldering involves a deeper chemical change that was actually the reason for me asking this question.

But if we can ENIG gold onto there, why do we still use the shitty caveman electroplating way where we need a connection? Well ENIG makes a pretty shit coating. It is enough to prevent oxidation, but is not smooth or long lasting. So for things like connectors where the gold plating has to stand up to friction of contacts, there you need something better. So those are still electroplated. PCB manufacturers tend to call this "hard gold" where all the pins on the connector are temporarily shorted together for plating, then the shorted area is milled away afterwards. Giving you a high quality durable gold finish.

I didnt know hard gold is electroplated, thanks for pointing that out.

You said ENIG is not smooth, I thought it is particularly used when a smooth surface is needed for BGA etc. What am I missing ?

[ebastler]

Off-topic question: What did you do to create the "@ebastler" reference? I didn't realize this forum software supports this, but find it quite useful. I got an (unobtrusive) notification that my name was mentioned, with a link to this thread.

Just typing @username does not seem to do the trick for me, and I don't see any other relevant icon in my post editor?

I think the term plating is important here, so either using electrical energy or not, this is the basic (chemical) process (ENIG or other type plating) and it differentiates it from soldering or HASL. So @ebastler 's reply makes sense to me.

[SeanB]

Smoother than HASL, but still is bumpy. Used because the nickel and gold plate protects the copper underneath from oxidising, so that the solder paste and flux application is more controlled in thickness, and thus the reflow step gets an even connection to all the BGA balls, and the flux is able to handle the slight amount of oxide that will have formed between manufacture and reflow. Thus the balls all will flow to cover the same area, and thus the package will be a consistent height above the PCB, so that you can not have balls that do not make contact, or some flatten out and short to adjacent ones. Plus afterwards you can easily wash flux residue out from under the package. The gold will dissolve into the solder, along with the nickel, and a little bit of the copper of the traces and pads, but there is not enough to make for a brittle alloy, so the joints will not fracture. Gold tin alloys have a certain percentage of gold that forms some very brittle alloys, so a thick gold plate can dissolve inot small volumes nad make the brittle alloy, or get the purple plague from the colour of the alloy in the fracture.

[metebalci]

Off-topic question: What did you do to create the "@ebastler" reference? I didn't realize this forum software supports this, but find it quite useful. I got an (unobtrusive) notification that my name was mentioned, with a link to this thread.

Just typing @username does not seem to do the trick for me, and I don't see any other relevant icon in my post editor?

Just added "@" before the username, lets try again, @ebastler

[ebastler]

Thanks, @metebalci. That's what I tried first, but it does not create an active link (mention) for me. Strange...

What client and editor are you using for the forum? Just the regular web browser interface for large screens? Using the "WYSIWYG" view in the editor or the one where you see plain text and tags? Or did you activate any non-default options in your user profile which I might not have found in mine?

[metebalci]

Thanks, @metebalci. That's what I tried first, but it does not create an active link (mention) for me. Strange...

What client and editor are you using for the forum? Just the regular web browser interface for large screens? Using the "WYSIWYG" view in the editor or the one where you see plain text and tags? Or did you activate any non-default options in your user profile which I might not have found in mine?

Indeed strange. I am using the regular web interface on PC, and the normal editor, not WYSIWYG I think, I see the plain text and tags. I dont remember if I changed something but I checked again and I dont see anything that might be related.

[jpanhalt]

Electroless plating definition (https://www.sciencedirect.com/science/article/abs/pii/B9780128035818091773):

Electroless plating has been defined as a controlled autocatalytic deposition of a continuous layer on a catalytic surface by the reaction of a complex compound and a chemical reducing agent.

Thus, it is a chemical reaction.  The term "conversion coating" may also be used.  I have seen that term applied mostly when the metal being plated  ("less noble metal") reduces the more noble metal ions in solution without added reducing agents.  Once it has a thin layer, its surface is no longer available to cause further reduction of the "more nobel" ions in solution.  Hence, the plating is quite thin.

As explained further in the above link, one can add other reducing agents and get thicker layers.  The base material does not have to be solely responsible for donating electrons (reducing) to the metal ions in solution.  "Tollens" reagent is an example of electroless plating on an inert surface using an additional reducing agent.

Dipping in molten solder does not involve a REDOX chemical reaction to get the coating.  It  is more similar to dipping a string in molten wax to make a candle or painting than it is to electroless plating.  No chemical conversion is required to get the coating.  In painting, however, the hardening or curing of the coating may involve a chemical reaction.

[ebastler]

Indeed strange. I am using the regular web interface on PC, and the normal editor, not WYSIWYG I think, I see the plain text and tags. I dont remember if I changed something but I checked again and I dont see anything that might be related.

Mysterious... When you quote my posts, the "@username" references in those become active mention links too. You must have super powers. Climbed any buildings lately? 

[metebalci]

Indeed strange. I am using the regular web interface on PC, and the normal editor, not WYSIWYG I think, I see the plain text and tags. I dont remember if I changed something but I checked again and I dont see anything that might be related.

Mysterious... When you quote my posts, the "@username" references in those become active mention links too. You must have super powers. Climbed any buildings lately?