External micro-PIXE analysis of the metal deposition on a CMS pitch adapter M. Massi, L. Giuntini, M.E. Fedi, C. Arilli, N. Grassi, P.A. Mandò, A. Migliori, E. Focardi Dipartimento di Fisica and I.N.F.N., Firenze, Italy The PA consists in a fan of metallic strips engraved on a glass support; the strips consist in an aluminium coating (nominally  400 g·cm -2 ) over a very thin chromium layer. Each strip ends with pads for the micro-bonding contacts. Al SiCu The Florence external micro ‑ PIXE facility appeared to be suitable to point out this kind of impurities: - good space resolution; - simple operation (external beam); - beam raster system integrated with a mechanical sample scan (system implemented by Oxford Microbeam Ltd.); - multi ‑ element capability and high sensitivity. Measurement conditions: - proton beam energy of ~3 MeV; - current up to 1 nA on the target; - ~12 m FWHM after 2 mm helium path. Problems on micro-bonding in a pre-production series of PA… … might be explained assuming the presence of metallic contaminants in the aluminium deposition. We analysed an overall 660x660 m 2 area: Copper contaminates the depositions and it is absent outside; Silicon is clearly coming only from the substrate (no contamination is present in the deposited material); Aluminium is a major constituent of the deposit, but seems to be present also in minor quantity on the substrate, which is reasonable; Chromium is the “glue” between the glass support and the glass deposition. The Compact Muon Solenoid (CMS) is one of the two multi-purpose detectors to be installed at the Large Hadron Collider (LHC), now under construction at CERN, in Geneva, Switzerland. the scanned area corresponds to 2x2 adjacent square maps of 360x360 m 2 (each obtained by beam scanning) with a 60 m overlap for a safer linking of the individual beam scans. The X-ray detection system consists in two Si(Li) detectors: one dedicated to lower energy X-rays (a helium flow was maintained in front of it) and the other optimised for the higher energy X-rays. We quantified the Cu contaminant from the spectra pertaining to selected sub-areas corresponding to the pads, by comparison to a thin standard and neglecting matrix effects in the metal deposit. The mean copper areal density comes out to be around 180 g·cm -2. Contamination from the target holder of the electron gun? 660 m Part of pitch adapter Optical microscope photograph and elemental maps of fan-out side From the silicon sensor (fan-out side) We also analysed a “good” PA from a different batch, on which the micro-bonding connections had resulted to be satisfactory: we detected no copper in the pads (having a sensitivity limit lower than 0.2 g·cm -2 ). The role of copper in the micro-bonding problems is clear. To the readout electronics (fan-in side) Cr Al Si Cu 660 m Optical microscope photograph and elemental maps of fan-in side Cr 1 mm The Pitch Adapter (PA) is a device situated between the silicon sensor and the front-end hybrid in the silicon tracker of the CMS experiment. Its purpose is to make the micro ‑ bonding connections possible between the input of the readout chips and the silicon sensor. BY OUR EXTERNAL MICRO-PIXE SET-UP WE HAVE BEEN ABLE TO IDENTIFY THE CAUSE OF UNRELIABILITY OF A DEVICE TO BE EXTENSIVELY USED IN LHC EXPERIMENTS AT CERN