Delamination is one of the most critical material defects in PCB technology. It describes the unwanted bursting or detachment of the copper layers from the base material (usually FR4) or between the individual prepreg layers. As printed circuit boards consist of a composite of different materials that have different coefficients of thermal expansion, the adhesion between these layers is crucial for the function and durability of the entire circuit board.
Causes of delamination: Heat, moisture and process errors
The main cause of delamination is thermal stress, especially during uncontrolled soldering (reflow soldering). When moisture trapped in the PCB suddenly evaporates, vapour pressure is created which pushes the layers apart - the so-called 'popcorning' effect. However, insufficient curing of the prepreg material during the manufacturing process or mechanical stresses can also weaken adhesion in the long term.
Consequences of delamination: From impedance fluctuations to total failure
A delaminated PCB loses its mechanical integrity. This often results in invisible cracks in the conductor tracks or via connections. This leads to intermittent faults (loose contacts), increased contact resistances or, in the worst case, complete power failure of the component. Particularly in high-frequency technology, the impedances change due to the inclusion of air, which massively disrupts the signal integrity.
Avoid delamination through correct storage, processes and drying
PCBs should be stored in airtight packaging in a dry place with a relative humidity of less than 50% at a temperature of 18 - 22 degrees Celsius.
It is important to adhere to the maximum soldering profiles and to select high-quality, high-Tg material (temperature-resistant base material) for applications with high thermal requirements.
To avoid delamination, the PCBs should be dried immediately before processing to remove moisture. The temperature and the holding time during drying are determined by the base materials / layer structures used. High-Tg, multilayer, flexible PCBs and rigid-flex PCBs have a higher moisture absorption.
Flex PCBs in particular must be dried before assembly (typically 130°C-150°C for 2-4 hours), as polyimide is particularly sensitive to moisture (hygroscopic).
see Drying / tempering of printed circuit boards
FAQ: Delamination of printed circuit boards
It is often visible to the naked eye: white spots or blistering between the layers, especially after soldering. In severe cases, the circuit board bulges visibly (blistering). A gap between the copper and the base material can be recognised microscopically.
As a rule, no. Once the material bond has been destroyed, the adhesion cannot be restored. The affected circuit board must be regarded as scrap and replaced.
Standard FR4 is susceptible if it has been exposed to moisture and extreme temperature peaks. High-Tg materials (higher glass transition temperature) or polyimide are significantly more resistant to thermally induced delamination.
Both terms are often used synonymously, but describe different degrees of severity. Delamination refers to the separation of the layers on the inside. Blistering is the visible manifestation of this - i.e. the formation of bubbles on the surface or between the layers.
The most important step is pre-baking the PCBs before soldering to remove any trapped moisture. In addition, the specified temperature profile of the circuit board should be adhered to exactly in order to avoid thermal shock.