1. Browning timeout fails
Browning refers to the process of copper surface treatment on the inner core board, and micro-etching on the surface of inner copper foil to generate an extremely thin and uniform organic metal conversion film  to enhance the joint force between copper foil and epoxy resin when the multilayer circuit board is pressed.Two key steps of brown treatment reaction equations are shown in (1) and (2) :
Copper etching reaction:
Cu+H2SO4+H2O2 - CuSO4+ 2H2O (1)
Film forming reaction:
Cu2+ + CuA +B - organic metal conversion film (2)
Where A represents the oxygen carrier and B represents the compound that can form the organic metal conversion film with copper oxide. The Browning process is shown in figure 3.
After gold and brown bonding, the veneer must be pressed together within 24 hours after Browning. However, the veneer takes a long time and is easy to exceed 24 hours, which will result in Browning failure and decreased binding force, leading to delamination, as shown in figure 4.
2. Brown film will change color at high temperature
The brown organic metal conversion film is dark brown, but the exposed brown film will change from dark brown to blue purple after the core plate passes through the lead-free reflow furnace.
Take five 100 mm x 150 mm copper clad, respectively marked as 1, 2, 3, 4, and 5, 1 after the normal brown not baking sheet, sheet 2, 3, 4, 5 respectively after the normal brown at 240 ℃, 250 ℃, 260 ℃, 270 ℃ baking 3 min, the brown shell color changes as shown in figure 5:
When the temperature reaches 270 ℃, the brown shell eventually fails, the brown shell composition changes over temperature ratio is shown in figure 6: [2