For cleaning the glue residue, you can use following solutions (alcohol wipes won't clean)
1) coleman fuel ( it is a black plastic bottle with red and white label any garden centres in uk sell them )
2) ronsonol lighter fluid yellow tin (not zippo)
( those two items listed above contains high percentage of PETROLEUM ETHER for samsung and iphone models it cleans without any problem
but some models of google nexus and they use different types of adhesive it won't clean )
If you can't get hold of those two listed above
3) isoproply alcohol (rubbing alcohol ) bit hard for iphones but better for samsungs
4) diluted acetone
And also thinner the layer better the result
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