Abstract: The invention relates to electronic components on thinned substrates, for example image sensors. Preferably, connection pads are connected through the thinned substrate to underlying layers and notably to a test pad by way of openings through which the metal of the pad passes. The openings are elongate openings extending along one edge of the pad of rectangular shape and a circular area of at least 50% (and preferably 65 to 75%) of the area of the pad contains no opening for connection with the underlying layers. This circular area is intended for bonding an external connection wire. The connection pads are testable from the back side by test probes and the front side may be tested (before bonding and thinning) by test probes with the same geometric configuration.