Testing a Lead Free HASL PCB
One of my new projects is to make a steno keyboard based on the type of high resistance circuitry the
Makey Makey uses.
I usually have PCBs made using the cheapest finishing option, leaded HASL. HASL is Hot Air Solder Leveling, essentially a layer of solder coats the copper traces. Copper is reactive and will corrode if left exposed to the air, the solder protects it.
Since this project will have fingers in physical contact with the HASL coating I chose the Lead Free HASL option. It was only a few dollars more.
I used a 3M test to see if it contained lead.
I bought the 8 pack from Amazon. The reviews on Amazon were mixed. It can produce false positives. The only good result is a negative result which would indicate that there is no lead, a positive result may not mean lead is present.
They look like cigarettes.
It is a cardboard tube with a plastic tube inside. The tube has 2 glass vials that are broken when you squeeze the tube (you aren't supposed to take it apart like I did.) Then you squeeze the mixed liquid out the white fibrous tip.
The 8 pack also came with 2 test cards. (One shown here.) This is to verify the test worked by triggering the lead reaction.
In short, it didn't work. Whatever the chemical reacts with turned it dark brown immediately on contact with the lead free HASL. So the test is useless in this application. If it remained white then there would be no lead. If it turned light pink, there might be lead. Turning dark brown is not something it is supposed to do.
Almost black.
I did another test on a leaded HASL PCB and it did turn pink (hard to see but it is a light pink.) So the test does detect the lead in that PCB, which definitely does have lead. Next to it in the picture is the dark brown test from the lead free HASL test.
Using the verification card the leaded HASL turned a uniform reddish color, as is should. The brown lead free test was already so dark I couldn't see a difference after using the verification card.
So, is the lead free HASL really lead free? Probably, but this test can't prove it. I think I will splurge on a ENIG PCB on my next version of the steno board.
