On 03:39 PM 27/07/2001 -0700, Abd ul-Rahman Lomax said:

>Then make a solder mask expansion design rule to tent the pad for each 
>class as desired. Top and bottom masks can be subject to different design 
>rules by adding layer scope as the second term in the rule selection criteria.

Restricting with layer scope will work for surface pads only.  It is not 
possible to apply different mask expansions depending upon the layer, using 
design rules for multi-layer pads.  I have written on this subject quite a 
number for times in the past and believe it is a significant oversight in 
the behavior of the program.

There is no method in Protel of automatically tenting the top but not the 
bottom (or visa-versa) of a multi-layer pad/via using design rules.

I also do testpoints as single pin components.  They are 1mm round with a 5 
mil think arc radius 47.5 mil on a mech layer to allow easy determination 
of our desired 100 mil TP clearance (we also set up design rules to check 
for this).  The Protel TP finder does not allow you to specify minimum TP 
clearance so is not useful. As others have said the advantages of using a 
TP component are:
1) the TP is shown on the sch, which is a huge boon
2) full control of layer and tenting
3) testpoints can usually be located off vias (which one board stuffer has 
informed us is their preference where possible as it reduces the incidence 
of via barrels damaged by test probes).

Ian Wilson

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