Richard MacCutcheon wrote:- >We seem to have developed a gremlin in our registration dept. >A very large portion of scrap is attributed to NO Annular Ring (<.002"). > >Over 90% of our product is 8-layer GIL with 2 and 7 as ground planes. >Cores are .005 constructed of 1-106 and 1-2313. Prepreg is 2313. > >Layer to layer misregistration is around .005" on average. Artwork pad >sizes are .022" over the max acceptable hole size. Tooling seems to be as >tight as ever but in the last few weeks we have had an inordinate amount of >scrap due to NO Annular Ring. > >What is the best systematic approach to take in identifying the problem(s)? Hello Richard, The cause of the misregistration could be:- 1 Layer to Layer misalignment on the same core 2 Core to Core misalignment 3 Drill target accuracy for CNC drill 4 Image stretch or shrink 5 Random drill variation Sectioning can determine (1) or (2). (1) could be due to photographic tooling for imaging inner layers. Carry out checks on inner layers before pressing. (2) could be caused by inaccurate tooling for pressing. This can also be checked by pinning panels together before pressing and looking for misalignment between the cores. It should be easy to see with thin cores. (3) is critical and if you are seeing good registration between all layers on the micro-section, but the drilling does not match the inner layers, this could be due to inaccurate target scoping. If the image is rotated relative to the drilling, this will almost certainly be your target scoping or pinning. Pins must be absolutely vertical as you will get around 3 mil error for every degree off the vertical on a 3 high stack of 0.062" panels. The top panel is the worst. (4) is due to photography or laminate dimensional changes. You can overlay the inner layer image on the drill pattern to determine whether the right stretch factor has been applied. If the material is moving more than predicted, then new photoplots will be required. (5) is least likely as you would have identified that quite easily but is due to spindle run out, lead screw wear, or stack movement. Once you are certain of the cause, the corrective action should be easy to work out although maybe not so easy to implement. Good luck Paul Gould Teknacron Circuits Ltd [log in to unmask] Isle of Wight,UK