kopwin

If a Welcome Letter is expected, it shouldn't take anywhere near that long. There is a processing page from NVC that gives exact timeframes, it's usually only a week or two, although has jumped up a bit recently. 
 
OP, what does your case status say when you check it, and when was your I-140 approved?

I will advise you to be patient everything will be fine. 
The National Visa Center (NVC) sends a welcome letter to applicants after receiving their petition from USCIS. The welcome letter includes fee invoices, case numbers, and invoice numbers. The process of getting a welcome letter usually takes 30–60 days, but can sometimes take up to six months. 

Wow that's really fast! Congrats!

my mum got approved on 2 may 2024 and i received email on 7 may 2024. physcial letter came a week later. my dad is still no approved. filled for both of them on same day april 22 2023. i dont know its taking long for him. i also paid my fees on 11 may 2024 and now since monday i cant login to feel in the DS260 or any other forms. It gives me URL not registered error. anyone facing this.

Yes, if it says it has. Not long after I applied last year, and had my welcome letter in about a week, it shot up to 60 days for it. So it does go up and down. 

I've asked numerous reps about that status, and all of them said not to worry about it. I also contacted NVC last week and they have submitted a request to USCIS to get my file. I'll chat with Emma today. Thanks!

Ah, I see! That makes much more sense now, I thought something was really wrong if it had taken you nearly 4.5 years to get to this point. 😂

I'm sure you'll get it soon, don't worry! 

It's about a month, not that huge a delay, but if it becomes more than 2 months, then I'd say definitely contact NVC and USCIS (Emma) to ask about it.