adhesion of copper to solder mask

Hello,

We have designed a 160ball bga substrate. Now we want to use the same substrate for the 145ball version of the product. All are the same, the package size, ball pitch, solder ball size only the number of balls will change. We will use a new solder mask to cover the extra 15 solder mask opening. We were told that adhesion of copper to soldermask is weak compared to soldermask to prepreg. Is our plan feasible without causing relaibility concern.

Any comments will be greatly appreciated

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