Improved PCB-inspection: an Application of Loess

Keywords: PCB-inspection, Loess, surface estimation

Abstract: Process control on printed circuit boards (PCB's) involves measurement of the volume of a large number (5000, say) of small heaps of solder paste, that are used to fix the components on the board. The amount of solder paste in each heap is crucial to board quality: too much paste may cause components to short- circuit and too little paste may result in loose components. At Philips, a measurement machine has been developed that performs the measurement by optical means. A crucial prerequisite for accurate measurement is a good estimate of the warpage of the PCB as it is clamped into the machine. In the talk, we will evaluate the use of LOESS (see Cleveland and Grosse, Statistics and Computing, 1991: 47-62) to estimate board warpage. In addition, we will discuss some novel computational issues that arise in such a repeated application of LOESS.