Is it advisable to use lead-free PCB and solder paste on a first SMD assembly job?

Question

I am sending my first PCB design to Sunstone for manufacture and I need to decide whether to order the board finish lead-free. All of the components are lead-free, and I have not decided on solder paste. There are about 25 chips on the board and the smallest are 0803 and SOT143. The board size is 3.0x1.5 inches. I am planning to order a cheap IR reflow oven like the T962A. This is not a consumer product (it's a driver board for an IR laser used in scientific experiments). I understand that lead-free solder doesn't flow as nicely and requires higher temps, etc. Shoud I Go Green or should the additional usage complexity dissuade me from using lead-free?

Followup question: should I order a stencil for a board like this?

Answer 1

When you are doing reflow, leaded vs. leadfree does not really make much of a difference. Leaded has a lower melting point, but is you are using a reflow oven with a temperature profile, you will not really experience any difference.

You will notice a difference when hand soldering. Leaded solder is easier to work with especially if your soldering iron is so-so. It's kind of like driving with a stick vs automatic transmission.

Btw, you'll be surprised how much of a difference a really good soldering iron makes. I had a cheap no-brand soldering station for a long time. Last year I got a new one (i bought PACE, but there are other good manufacturers as well) and the difference is astounding.

Lead is actually poisonous and working with solder paste is more messy than solder wire. I have kids in the house and I use leadfree solder paste for reflow and anything commercial. I use leaded solder wire for the occasional hand soldering on prototypes.

Answer 2

While going green is a laudable goal, the real reason most firms go led free is because of legal requirements in places like Europe or California (USA).

If reliability is more important than green then why not stick with leaded solder, assuming of course that you are not requires by your customers to provide lead free or ROHS compliant product.

With lead solder you do not need to be concerned with "tin whiskers" which can cause your boards to fail in service. For more information see: http://nepp.nasa.gov/whisker/background/

As for a stencil, they are generally worthwhile.

Answer 3

I accidentally bought lead-free for my first tube of solder paste (and my first PCB reflow) and didn't have any troubles. I bought a few of those little breakout boards and some cheap components to do some testing before I did my actual board. My first try was a bit of an embarrassment... the breakout board turned into a pool of black goo. Lesson learned.

As for the stencil, I'd highly recommend using the soda can method. It doesn't require expensive equipment and will save you a ton of money in the long run if you're doing a bunch of prototyping. Just remember that everytime you change your design, the stencil likely needs updating. So don't bother wasting your money on a laser cut stencil, make your own.