The combined effort of several laboratories at our institution resulted in the building of the first dedicated, breast PET/CT prototype. Ongoing clinical trials for breast cancer diagnosis and assessment of response to treatment underlined the need of a second generation prototype with improved sensitivity and spatial resolution. The goals of the new prototype are to reduce scan time and partial volume effects on quantitative measurements of small lesions. Several designs have been proposed by our group and are currently under investigation at different levels. In this work, we present the complete characterization of a detector module for an intermediate generation breast PET prototype, together with its design and assembly. The proposed design consists of two heads, shaped around the circumference of a circle of radius 26 cm. Each head is formed by 2 rows of 8 modules each, each module consisting in a 14x14 array of unpolished LSO crystals, read out by a position sensitive photomultiplier tube (PSPMT). Crystal pitch is 1.5 mm. A complete characterization of two detectors modules in coincidence resulted in an energy resolution of 25.2%, a timing resolution of 2.4 ns and an average intrinsic spatial resolution for a central row in the array of 1.26 mm. The two detector heads are now fully assembled and connected to the electronics suite for data processing. Modification of the system electronics is underways and the first floods, showing excellent position encoding, are presented. A thorough evaluation of system performance will be completed in the next few months. We plan to combine this scanner with a third generation breast CT system currently under parallel development to form a new generation, dedicated breast PET/CT scanner.