To get this trophy you need to defeat the Saturn Mothership boss.
You will need to get to wave 79 and complete the wave, when in the store purchase as much shield as possible. You should also purchase 1 Smartbomb.
When you start wave 80 instantly hit L1 which will activate the smart bomb and instantly destroy all enemies in that wave therefore enabling you to go straight to the mothership battle without the possibility of losing any shields during the battle with normal enemies.