Hello All,
     
     I have three design questions open for discussion or debate.
     
     Please feel free to respond to any or all.
     
     1.) Circuit Routing Programs:
     I have seen several designs where traces are routed at the minimum 
     spacing, between two pads, when they could be routed differently to 
     optimize spacing. These are typically designs with multiple traces 
     running between pads. It appears the design algorithm will not 
     automatically jog a single or multiple lines to maximize the spacing.
     Do effective, reliable, high quality programs exist that could 
     maximize these types of designs?  Does the design community support 
     these programs, assuming they exist?  You can guarantee I would notify 
     the customer and let them review any changes prior to making 
     implementing any changes.   
      
     2.) Plated Hole/Trace Spacing:
     In an effort to increase density I have seen a few designs where non 
     functional pads have been removed from internal layers to rout the 
     traces closer to the holes.  The problem is that the traces have been 
     0.20 mm (0.0080) from the hole barrel.  Referring to Table 5-10, in 
     IPC-D-275 the minimum standard fabrication allowance is 
     0.25 mm (0.010).  Therefore, using this value I would predict the 
     minimum finished spacing I could assure the customer would be 0.08mm,
     (0.0030).  I subtracted half of the minimum standard fabrication 
     allowance from the minimum distance found between the trace and the 
     hole barrel.  Do you concur with this result?
     
     3.) Drill/Gerber Data Misregistration:
     It is more common to find customers who provide drill data and gerber 
     data which misregisters, approximately 1 out of every 5 jobs.  We 
     typically see this when Gerber data is provided in 2.4 format and the 
     drill data is provided in 2.3 format.  The amount of misregistration 
     has been 0.03 mm (0.0010).  We have also been told this 
     misregistaration can be a result of the design software used. The main 
     concern is this misregistration can effectively reduce your hole 
     location allowance by 33%, considering 0.25 mm (.010) DTP.  We correct 
     the errors but wonder if this trend will be improving.
     
     
     Thanks is Advance for your thoughts,
     
     Mark Santos
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