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Reflow soldering of lead-free components with leaded solder paste

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Emanuel:
I am confused about the parameters of the reflow profile needed to solder lead free components.
We assemble boards for automotive modules required with leaded solder paste. The boards have ENIG finish.
The problem is that I see some wetting issues, very erratic, can be a single resistor with one side not soldered, not in the same place and not the same one, so for sure is not a component oxidation.
The profile is set according to the solder paste manufacturer data sheet, however the dealer recommended to increase the peak temperature and bring it to the lead free level.
While this makes sense as the components pads are coated with lead free tin, this exceeds the solder paste limits.
The solder paste is SnPbAg.
I will appreciate any advise.

SMTech:
Curious, why are you using leaded paste? Even the automotive industry made that switch years ago for many areas, the exemption list gets smaller all the time. We assemble all sorts of automotive PCBs for dashes or adjacent functions and we have used lead free paste since ~2006.

Wetting could be an ENIG issue, or perhaps your paste needs to be slightly more aggressive. Either way you should perhaps run some tests, try the higher temp, try a higher melting point leaded paste or even try a HASL finish instead. Inspect the joints at a lab to check the metallic structures even.

Psi:
Not all ENIG is made equal, sometimes the amount of gold they add is as thin as they can get away with in order to save money.
Maybe the nickel is coming through in places.


Usually this is only an issue on the ultra cheap and dirty china pcb makers, but i'm not sure were you are getting your boards from.
Maybe they are skimping on the ENIG gold.

Emanuel:
There are manufacturers that require this, same as in other industries. In this case it is heavy duty vehicles.
The boards arrive with a test report and a sample of a soldered board, all the pads are well covered.
Also, as I mentioned the wetting problem of only one pad of the component is erratic, not on all boards, not on all the resistors of the same value/size and in different locations.
Yes, looking at some "statistics" there is a certain location where this is happening more often, near a SOT-263.
We started to use ENIG just 2 years ago because of 2 reasons:
There is no oxidation as with other options and compatibility with the leaded process, instead of fighting with both the PCB and the component now we only need to worry about the components.
It can be the ENIG, I was thinking about this.
The solder paste we use is KOKI SS48-M955, SnPbAg

Emanuel:
I am talking about something like this. (not my picture, found on the net)
The pad is well covered with solder but on one side the pad is just on top of the solder.

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