Programmatically create an object under different screen sizes

I am having the code below for creating an button.

Now the location of the button cannot be aligned or scaled correctly with different devices.

I wrote the following code under iPhone 6 screen size.

UIButton *but= [UIButton buttonWithType:UIButtonTypeRoundedRect];
        [but addTarget:self action:@selector(buttonClicked:) forControlEvents:UIControlEventTouchUpInside];
        [but setFrame:CGRectMake(605, 320, 35, 35)];
        [but setTitle:@"Login" forState:UIControlStateNormal];
        [but setExclusiveTouch:YES];
        [self.view addSubview:but];

If i want to have the same position for iPhone 6 plus as the iPhone 6. What can i do?

Many thanks.