The CALICE collaboration is studying high granularity and compact calorimeters for the future International Linear Collider. The electromagnetic calorimeter is made up of tungsten as absorber and silicon detectors implementing PIN diodes arrays. Calibration tests of a first prototype are describe first. Data taken in test beam environment have shown an unexpected behavior of the sensors found to be related to a crosstalk. This crosstalk is suspected to generate the so called "square events" seen in the test beam data where all bordering pixels of the sensor are illuminated. An analytic model is proposed to describe the crosstalk couplings within the sensors. Analytic results are compared with electrical simulation with the aim to understand forthcoming measurements on real hardware. A new design of guard rings is then discussed according to its impact on square events.