Lead-free flip chip bumping with special focus on stud bumping - A flexible and economical flip chip technology

Due to coming environmental legislations, lead-free flip chip technologies are gaining increasingly high focus. Of the various lead-free possibilities, stud bumping will be described in some detail. The flip chip stud bumping will shortly be explained together with the various joining technologies using either conductive adhesives or non-conductive adhesive pastes or films. The use of non-conductive adhesives (underfills) will result in and rely on a mechanical contact with the bump and pad held in compression due to the contraction or shrinkage of the adhesive after cure. Also metallurgical contacts - obtained by using solders or thermo-sonic or thermo compression bonding mil be described. Some focus mil be on the so-called SBBä - Stud Bump Bonding -technology which is based upon a conductive adhesive joint. Applications range from (mobile phone) CSPs, MCMs, SAW filters, MMICs, digital cameras, memory devices and hearing aids. Stud bumping addresses not only the very fast prototyping needs but also high volume, cost sensitive applications. Applications with stud bumping and in particular SBB on a variety of substrates - glass, thick film ceramic, LTCC, FR4, micro-via and flex - will be described, together with the obtained high reliability data.