If the data file is not too large you could slurp it into a single string and use a regex to pull out groups of lines with the parts to concatenate in separate memory groups.

use strict;
use warnings;

open my $dataFH, q{<}, \ <<END_OF_FILE or die qq{open: $!\n};
library_AND
PIN.A
DELAY_TABLE 1 20 2 40 3 60 4 65 5 75;
DELAY_TABLE 1 10 2 15 3 45 4 70 5 80;
POWER_TABLE 20 30 40 50 80 97 110 20;
POWER_TABLE 3 4 5 6 10 80 90 10 20;
library_BUF
PIN.B
LEAKAGE 1 2 3 4;
TRANSIT 1.1 2 3.4;
END_OF_FILE

my $dataString = do
   {
       local $/;
       <$dataFH>;
   };

close $dataFH or die qq{close: $!\n};

my $rxGroup = qr
   {(?xs)
       (library_[^\n]+)\n
       ([^\n]+)\n
       (.*?\n)
       (?=(?:library_|\z))
   };

while ( $dataString =~ m{$rxGroup}g )
{
    print qq{$1:$2:$_\n} for split m{\n}, $3;
}
[download]

Here's the output.

library_AND:PIN.A:DELAY_TABLE 1 20 2 40 3 60 4 65 5 75;
library_AND:PIN.A:DELAY_TABLE 1 10 2 15 3 45 4 70 5 80;
library_AND:PIN.A:POWER_TABLE 20 30 40 50 80 97 110 20;
library_AND:PIN.A:POWER_TABLE 3 4 5 6 10 80 90 10 20;
library_BUF:PIN.B:LEAKAGE 1 2 3 4;
library_BUF:PIN.B:TRANSIT 1.1 2 3.4;
[download]

I hope this is useful.

Cheers,

JohnGG

Update: Removed superfluous my $group = from while clause, left over from earlier version. Original line was

while ( my $group = $dataString =~ m{$rxGroup}g )
[download]