Delamination
Delamination turns up in 4 fields: thermal spray, PCBs, concrete, nonwovens. Here is what it means to the people in each one.
Delamination in thermal spray
Separation of a coating from its substrate or of one coating layer from another.
Loss of adhesion at the bond line or between layers, showing as blisters, lifted areas or sections that peel away. Root causes include poor surface prep, contamination, insufficient profile, high residual stress from thick or hot-sprayed layers, dusting between passes and thermal mismatch. It is checked by tapping, bend tests on coupons, visual and dye-penetrant inspection and cross sections.
"Coating's ringing hollow when you tap it, there's delamination under there, strip it."
Delamination in PCBs
Separation between layers of a board's laminate or between laminate and copper, usually from heat or moisture.
Delamination is the splitting apart of layers inside a board: glass from resin, prepreg from core, or copper from laminate. It shows as blisters or bulges after reflow or rework, often when absorbed moisture turns to steam, when the board passes its decomposition temperature, or when lamination was poor. Acceptance criteria tolerate only small, isolated blisters that leave conductor spacing intact, because spreading delamination breaks traces and plated holes and opens paths for leakage.
"Board blistered next to the BGA after the third rework cycle, that's delamination, scrap it."
Delamination in concrete
A surface layer that has split away from the concrete below it, found by the hollow sound it makes when tapped.
In new slabs, finishing delaminations form when the surface is densified before trapped air and bleed water escape, leaving a thin layer that sounds hollow and later breaks loose. In bridge decks and garages, delamination is a horizontal crack at the rebar level driven by corrosion, located by dragging a chain or tapping with a hammer and listening for a drummy sound. Both end in spalling if left alone.
"Chain drag found delamination over about a third of the deck, mostly over the top mat where the cover's thin."
Delamination in nonwovens
Separation of the layers of a laminate or multilayer nonwoven, such as an SMS or a film composite.
Delamination happens when the bond between layers is too weak for the stresses of converting or use, from too little adhesive, too cool a calender, contamination or incompatible materials. It shows up as bubbles, peeling or layers splitting at cut edges. Peel strength tests measure the risk, and the defect is a frequent source of customer complaints.
"SMS is splitting into layers at the slit edge, that's delamination, bring the calender temperature up."