Commonwealth Bank will pay 140 basis points over the 30-day bank bill swap rate on the top tranche of its latest issue of residential mortgage-backed securities. CBA has upsized the deal from A$750 million to $1 billion.The $920 million of class A notes, which have a weighted average life of 3.54 years, are priced at 140 basis points over swap. The notes have indicative AAA ratings from Fitch and Standard and Poor's.The A notes have eight per cent credit support, while 14.8 per cent of the portfolio is covered by lender's mortgage insurance.Pricing on the class B and C notes was not disclosed. The $60 million of class B notes have a weighted average life of 5.15 years and the $20 million of class C notes have a weighted average life of 9.42 years.The last big bank to issue RMBS was Westpac, in May, when it priced the A notes of a $1.15 billion issue at 140 basis points over the 30-day bank bill swap rate.