Well the way I understand how boards are made is they are a fiber glass substrate that is bonded with a resin to stiffen the board , the board is then heat treated , circuits and other items are attached then its slightly floated over a river of solder to bond the compactors and other items to the board then heat treated once more and sealed , then off to testing . I am thinking that the board and the sealing risen is breaking down and expanding from heat and depending on age of the unit oxidation of the metals , not all mother boards are made the same way chemicals different from company to company and such . hope this helps .