A pixel detector consists of an array of radiation sensing elements which is connected to an electronic read-out unit. Many different ways of making this connection between these two different devices are currently being used or considered to be used in the next future. Bonding techniques such as flip chip technology can present real advantages because they allow very fine pitch and a high number of I/ Os. This paper presents a review of the different flip chip technologies available and their suitability for manufacturing pixel detectors. The particular problems concerning testing of pixel detectors and thermal issues related to them are pointed out.