"becomes obvious when" is correct and usable in written English.
You can use it when you want to indicate that something has become clear through the preceding context. For example, "His incompetence becomes obvious when he tries to explain the problem."
The O 2s peak is attributed to the Ga O and Al–O bonds, and it becomes obvious when the detection angle is becoming larger.
It becomes obvious when they reach Saturn: how do they slow down?
It's about silence, and how different cultures value or don't value it — a nuance that becomes obvious when we travel.
As most computer users already know, poor resolution becomes obvious when the font size on the computer screen increases.
The importance of odour in the common concept of taste becomes obvious when a person has a cold and can no longer "taste" food.
"Yet the scale of the discrimination becomes obvious when news of a church being built is hailed as such a monumental event".
How bold it was becomes obvious when you hear Ronaldinho insist that he feels Milan's owner, Silvio Berlusconi, treats him like a special son.
That becomes obvious when parents are invited in to talk about the problems and can't control their own behaviour to the extent that, on occasions, they have to be escorted off school premises".
This cruelty doesn't exist in isolation, as becomes obvious when the father of one of the other accused rapists contacts Mija and sweeps her off to an afternoon meeting at a restaurant.
But as becomes obvious when the heavily bearded Rick gets a shave, a haircut and a hot meal (with his monthly government stipend), the homeless have the same human face as the rest of us.
Despite the intense, urgent feelings that pulse through its pages, this novel of emotional realism is based on an emotional fantasy — as becomes obvious when Morris is forced to conclude it with an unconvincing denouement.
