Richard, Great discussion. No, I haven't found trace thickness to be of any significant clearance issues. But, then, I've only worked as high as 2 oz Cu. Nothing higher.
I have no experience with IEC 664-1. Sorry. Regards, Doug Richard Steele wrote: > > Doug, > > > Situation A : Board is continuous between trace A > > and trace B. That is to say, there > > is FR4 material between the traces. > > > > ---------------------- > > ------ ------ > > | A | | B | > > ------ ------ > > ---------------------- > > We have treated this as a cemented joint and have achieved an electric > strength >5kV for a 6 thou spacing (inner layers only). It's the outer > layers where creepage (and to some extend clearance) becomes applicable > with around 1kV for a 6thou spacing. > The creepage increased from 1kV @ 6thou to 2.3kV at 60thou whereas the > clearance increased from 980V @ 6thou to 5kV @ 54thou. > Different samples gave slightly different results, this may be to do > with the fibreglass weave grain and surface contamination. > > > > > Situation B : Board is NOT continuous between trace A > > and trace B. That is to say, there is an > > air gap cut through the board between > > the traces leaving the traces exposed. > > > > --------+ +----------- > > ------| |------ > > | A | | B | > > ------| |------ > > --------+ +----------- > > > > Clearly, even on an unpopluated board fab, > > Situation B is strictly a clearance issue. > > Haven't used this scenario and can't think when we would, but yes in > this situation clearance is more applicable than creepage, dependant > upon the distances involved. > > > I assume you're talking 1 or 2 oz copper for your traces? > > Generally 1oz but greater on PSU's, have you found that the thickness > alters the creepage/clearance greatly? > > What relevance are the creepage distances quoted in IEC 664-1 Table 4 > column 2 for printed circuit material, do these assume a CTI of >600 > (Material Group I)?, if so this has not been stated. > The IEC 664-1 creepage figures differ greatly from those in IEC 950 for > PCB material. Where did these come from and what can they be used for? > > Are there any creepage and clearance experts out there? > > Regards > > Richard Steele > Equipment Engineering > Fujitsu telecommunications Europe limited
