The way you should do test points is not to use vias. Setup a library component with a square pad with solder mask relief, no solder paste, and set the component in the library to be a testpoint.
Then in the software press a button to export an Excel list of all components setup as testpoints with x, y locations (from a specified origin), the type of testpont and names.
This would be a very useful feature to go on your future todo list.
(disclaimer: I am a test engineer)
not correct.
You do NOT want to drive the testpoint from the schematic. This blocks an efficient use of available space. Depending on the tester ( some testers are top only, some are bottom only , some do both, ) and the probing technology used , you let the tool assign the test points as much as possible on existing via / pads. the tool needs to be aware of the probe to body ( given by the radius of the probe tip + an offset ) and the inter probe pitch ( given by the density of the probes and the size of the probes )
The layout software will assign as much as can be done. the ones that are 'unfittable' then get placed as free pads either on top or bottom , or additional via's are plonked down.
@iliya : the implementation you have now for via's is not flexible enough. Simply let us specify start layer and end layer. that allows for all technologies to be used.
draw such via's (that are not top to bottom ) as two half circles, one with the color of the starting layer, one with the color of the ending layer. so we visually can tell by looking at a via which layers it bridges. if it is a simple thru via simply color it grey. if it is anything but a simple : draw the two-color structure ( still a circle but one half filled with start layer colro , one half filled with end layer color , then draw the hole size over that structure.
given a 8 layer board :
if you need a simple thru-hole via : top to bottom
need a laser ? set it top to inner 1, or top to inner 2, or bottom to inner 6 or bottom to inner 5 ( 1 hop or 2 hops )
need a buried one ? inner 2 to inner 4 ( for example )
need stacked ? inner 2 to inner 3 , and a second via at same coordinates inner 4 to inner 5 )
need backdrilled ? top to inner 4 for example.
make sure the program understands layer 'pairs'.
for a 4 layer board you can only make the following bridges :
1-4 : thru
1-2 : laser
2-3 : buried
3-4 : laser
1-3 or 2 to 4 by making a 1-4 and then backdrilling
for a 6 layer board you can only make the following bridges
1-6 : normal via
1-2 : laser
2-3 : drill
4-5 : drill
2-5 : drill
5-6 : laser
the above is based on a 2 core stackup with an inner prepreg and outer lamination.
if you change this to sequential lamination then the rules change. the software needs to be aware of this. ( sequential lamination for more than 6 layers is expensive as the yield drops due to registration errors)
a 6 layer board is made as two double sided boards first ( one core each )
so you get
single layer board layer (1)
prepreg
double sided board layer 2 and 3
prepreg
double sided board layer 4 and 5
prepreg
single layer board layer 6
so you can drill 2 to 3 and 4 to 5 as these are each one core.
once that stack is made you can drill 2 to 5 as you have a stack of core 1 (layers 2 and 3) , prepreg , core 2 (layers 4 and 5)
so you can drill that.
then you apply prepreg and foil . now you can mechanically drill 1 to 6
you can now backdrill ( from an outer layer to any inward layer ) . note that backdrill REMOVES the plating in the hole !!! backdrilling is used in high frequency boards to remove stubs.
you can now laser from top to inner 2
this is difficult to explain in words. i need to draw a sketch how the lamination sequence works and what can be drilled when.
the rule of thumb is :
- mechanical drilling happens across cores so it is always an EVEN number of layers. you cannot drill '3' layers'.
- lasering is outer layer to 1 layer , or 2 layers below. this allows stacked / blind. they laser inner 1 before laminating the outer foil, then laser again. such holes are 'blind' : you do not see a hole in the pad as it is grown shut.
a buried via is a via that is capped : there is still a physical hole there but it is covered on both sides by pre-preg. so you can not see the copper or the hole from the outside.
a blind via is a via where you can see the copper form the outside. you do not see the hole as it is filled with copper. these are typically lasered via's.
there is a tendency in the industry to move towards laser via's more and more as it is much cheaper. Laser drills shoot almost 1000 holes a second.... on a mechanical drill that takes well over 30 minutes to do ... but , laser drills can only go 1 or two layers ( they can only shoot 1 layer at a time , but you get two deep due to the lamination step on the outer layers , so you can shoot twice. the reason behind this limit is the diffraction of the laser as it strikes copper. it bounces upward and destroys the prepreg.
in other words :turn on the laser , hitting copper first , then drill pre-preg until you strike copper again. the moment you get the second reflection you turn off the laser avoiding damaging the prepreg in between the copper layers.
on sequential lamination you can keep lasering as you have no 'core' apart from the initial start in the center of the board.
again ,this is complex material and needs to be explained with a drawing.
Stacking cannot be done mechanically, only using laser