Nouvelle pâte PP 2793 de bouchage pour les substrats haut Tg

En plus de la pâte de bouchage PP 2793 utilisée pour les substrats FR 4 standards, nous sommes maintenant….

The thermo mechanical properties of the new materials are aligned to the ones of high Tg Epoxy Substrates to minimise the thermal mismatch between the substrate and the Plugging Paste for optimal reliability.

To ensure long term reliability it is mandatory that the properties of substrate and the plugging material match to reduce mechanical stress caused by different coefficients of thermal expansion (CTE). The properties to observe are the glass transition temperature (Tg), the CTE (below Tg) and the CTE (above Tg).

In case of via hole plugging the critical factor is the z direction, since here the effect of thermal expansion has the highest impact due to the stress applied on the PTH barrel and the cap plating. Concerning the mechanical stress the Tg is the most critical parameter, since the CTE of the epoxy based resin systems (Substrate in z axis orientation) and the plugging material are usually in a very similar range, whereby the high Tg materials show slightly smaller CTE values.

A mismatch of the Tg will cause increased differential expansion of the materials in the z axis direction and lead to fatal defects like barrel cracks or delamination of the cap plating. The use of a plugging material designed for standard laminate in a PCB build with high Tg laminate will cause a mismatch >30% for the differential CTE z 40-240 and represents a serious thread to thermal reliability.

The new PP 2793 can be applied by screen- or stencil printing, by roller coating and vacuum plugging equipment as e.g. the MASS VCP 5000. The long shelf life of 6 months at room temperature allows optimal processing on these units and avoids material loss due to frequent cleaning of the equipment.

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