Composition for forming a copper-containing interlayer comprising internal pores

A composition for forming a copper-containing interlayer between a first solid substrate and a second solid substrate, which composition comprises the following components:

• an organic binder;
• and
• flakes of copper or a copper alloy, wherein:
• the flakes comprise internal pores,
• the flakes have a multi-layer lamellar structure,
• the internal pores are totally surrounded by the copper or the copper alloy,
• any one of the internal pores has a diameter in a range of 2 nm to 30 nm,
• the flakes have a mean particle size D50 determined by laser granulometry of at most 5 μm,
• the flakes comprising internal pores have a mean intraparticle pore density in a range of 2 internal pores/μm2 to 30 internal pores/μm2 in an arbitrary section through any of the flakes,
• the multi-layer lamellar structure comprises or consists of at least two and of at most 20 lamellas,
• any one of the lamellas has independently from each other a thickness in the range of 5 nm to 20 nm,
• the organic binder is a terpineol, a primary alcohol, a diol, a triol, a polymeric glycol or a mixture of at least two of a terpineol, a primary alcohol, a diol, a triol and a polymeric glycol,
• the total weight of the flakes is at most 80 wt. % of the total weight of the composition,
• the remaining part of the composition is formed by the organic binder, and
• the mean intraparticle pore density of the flakes of copper or the copper alloy is determined by:
• embedding the flakes in a resin,
• preparing ultrathin sections of the embedded flakes,
• taking transmission electron microscopic (TEM) images and/or scanning electron microscopy (SEM) images of the ultrathin sections of the embedded flakes,
• determining a plurality of intraparticle pore densities by calculating the number of internal pores within the ultrathin sections of the flakes in relation to the total area of these ultrathin sections of the flakes, in a plurality of TEM images and/or in a plurality of SEM images, and
• calculating the mean of the plurality of intraparticle pore densities determined in this way.