PCB footprint recommendations for FPC soldering

If this is for production access only, then here's a trick I used once. The PCB (standard 0.062" thickness) was designed with SMT pads along one edge (both sides) so that a 2×7 0.100" JTAG header could be soldered to it, with the pins sticking out from the edge. This was useful for debugging prototypes, which needed more or less constant access to the JTAG (and weren't in cases).

In production, the connector is omitted, and I used a slightly modified DIP clip to access the pads for the connector. I just needed to bend the contacts inward a bit to get adequate friction and contact pressure.

Instead of the DIP clip, you could use a standard card edge connector as well.

Some useful information about different types of solder: NIST Metallurgy

The main important tables are 1.12 (coefficient of thermal expansion/elastic properties of leaded solders) and 1.14 (tensile/shear strength of leaded solders).

I believe the document has information for lead-free solders as well (that is what it is called after all), I didn't look too hard for these.

The key properties for 63/37 leaded solder:

Coeff of thermal expansion: $$ \alpha = 24 \frac{10^{-6}}{K} $$ Elastic Modulus (I'm using the 20 degree figure, it will be slightly higher near 0 degrees, not exceeding 38.1 GPa at -70 degrees): $$ E = 30.2 GPa $$ Tensile strength: $$ \sigma_{max} = 56.19 MPa $$

The worst case scenario is if the solder is mounted onto something completely rigid. Suppose we were to take the 0 stress state as room temperature (25C).

The contraction due to thermal expansion is:

$$ \epsilon = \alpha (25C - 0C) = 0.0006 $$

And the appropriate tensile stress is: $$ \sigma = E \epsilon = 18.12 MPa $$

This is well below the tensile strength of the solder.

However! Even better is that the PCB board itself will contract with the solder as it cools down. Depending on the actual layup direction, this closely matches the 63/37 solder CTE (~20e-6/C for the primary direction), so the actual stress will be lower.

tl;dr: you'll be fine. You might have to worry more about moisture/condensation, as well as having components which are rated for below 0C operation instead of worrying about solder joints cracking.