I have a coupon for Google Adwords, after the coupon and its amount runs out will Google start to charge my card automatically?

The reason i ask this is because before you can submit any coupon code you must enter billing details so i am a little worried that google is going to charge my card after the coupon runs out automatically, i dont want this to happen and i want to see how good google ads is before i actually buy any more.

Looking forward to hearing your answers.

Thanks.

David.