AM5 is the DDR5 2channel desktop socket for AMDs CPUs
FL1 is the DRR5 2channel “laptop” that supports the same AMD CPUs but packaged by soldering (BGA instead of LGA)
Back in the DDR4 days, AM4 laptops used to exist (see https://www.xmg.gg/en/news-xmg-apex-15-max-e22/), but AM5 laptops do not exist, instead being replaced by FL1 (from what I can tell)
This is both wasteful from AMDs side (creating new SKUs) and from the consumer side (not being able to upgrade, and having to wait for BGA cpus to be released, for example zen5 are not out yet while AM5 zen 5 has been out for a while)
Is this done to get a saving 0.5mm of thickness, or are there any other benefits
The space savings are substantial when going to BGA, many tens to hundreds of mils. Beyond the space savings there are very meaningful performance and efficiency improvements by ditching the socket.
CPU-socketed laptops have always been around, but are rightfully becoming less and less popular as time goes on and their shortcomings shine brighter.
I have not found any evidence that the socket itself causes higher power consumption (in the theory the higher resistance of the socket could contribute to the power loss, but in practice that should be insignificant to the power consumption of the CPU)
Its not so much the high resistance that causes the increased energy consumption for a given switching frequency, its the increased impedance of LGA vs BGA.
All the little structures in LGA pins cause all sorts of reflections and raise the impedance over what BGA offers, which necessitates running signaling at a higher voltage to get the same signal integrity on LGA vs BGA.
FL1 is not really a socket, it’s a package type. Since a CPU used in an FL1 (BGA) configuration is already different from an AM5 CPU, it’s by default not used in the same applications. So, AMD moved from Zen3 to Zen4/5 CPU architecture and therefore the BGA equivalent is different. Comparing an LGA socket to anything BGA is useless, they’re apples to oranges unless you’re really asking why does BGA exist and in that case, it’s obviously a more attractive package type for compact computers that rarely see upgrade paths or that need to be extremely compact, like a SFF or mobile systems.
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FL1 and AM5 CPUs use the same chiplets packaged with the same architecture (1 IO die + 2 Core dies)