Real-time control of via stub drilling depth asymmetry
A gang drilling machine for drilling a circuit card includes a pair of n and p master drills that are configured to be aligned in registry with respective n and p test vias of the card; pluralities of n and p minion drills that are configured to be aligned in registry with pluralities of n and p live vias of the card; and a controller that is electrically connected to control the n and p master drills and minion drills, and to send and receive electrical signals to and from the card. The controller is configured to: send a query signal to the card; monitor a response signal from the card; determine drilling depth of at least one of the master drills, in response to comparing the response signal to the query signal; and adjust operation of the machine, in response to the determined drilling depth.
1 . A gang drilling machine for drilling a circuit card, the machine comprising:
an n master drill and a p master drill forming a pair configured to be aligned in registry with a respective n test via and p test via of the circuit card;
the n master drill associated with a plurality of n minion drills and the p master drill associated with a plurality of p minion drills, the plurality of n minion drills and the plurality of p minion drills configured to be aligned in registry with a respective plurality of n live vias and a respective plurality of p live vias of the circuit card; and
a controller that is electrically connected to control operations of the n master drill, the p master drill, and the associated pluralities of n and p minion drills, transmits and receives electrical signals from the circuit card, wherein the controller is configured to:
send an electrical query signal to the circuit card, wherein sending the electrical query signal comprises sending an n query signal to the n test via and sending a p query signal to the p test via;
monitor an electrical response signal from the circuit card, wherein monitoring the electrical response signal comprises monitoring an n response signal from the n test via and monitoring a p response signal from the p test via;
determine a drilling depth of at least one of the master drills, in response to a comparison of the response signal to the query signal, wherein determining the drilling depth comprises:
measuring a stub length time skew between the n response signal and the p response signal; and
determining a stub length offset between the n test via and the p test via, in response to the stub length time skew; and
adjust operation of the gang drilling machine, in response to the drilling depth, wherein adjusting operation of the gang drilling machine comprises increasing the drilling depth of the at least one of the master drills and the plurality of associated minion drills, in response to the stub length offset.
2 . The gang drilling machine of claim 1 , wherein the controller is configured to;
increase the drilling depth of the n master drill and the plurality of n minion drills, in response to the stub length offset indicating that the n test via is longer than the p test via.
3 . The gang drilling machine of claim 2 , wherein the controller is configured to:
increase the drilling depth up to a maximum design value.
4 . The gang drilling machine of claim 1 , wherein the controller is configured to:
increase the drilling depth of the p master drill and the plurality of p minion drills, in response to the stub length offset indicating that the p test via is longer than the n test via.
5 . The gang drilling machine of claim 4 , wherein the controller is configured to:
increase the drilling depth up to a maximum design value.
6 . The gang drilling machine of claim 1 , further comprising the circuit card.
7 . The gang drilling machine of claim 6 , wherein the circuit card comprises:
a test coupon portion of the circuit card; and
a live portion of the circuit card;
wherein the test coupon portion comprises:
the n test via;
the p test via; and
n and p test ports that are electrically connected to the respective n and p test vias; and
wherein the live portion comprises:
the plurality of live n vias; and
the plurality of live p vias.
8 . The gang drilling machine of claim 7 , wherein the test coupon portion comprises a first test coupon portion and the circuit card further comprises a second test coupon portion that is laterally offset from the first test coupon portion, wherein the live portion is disposed laterally between the first test coupon portion and the second test coupon portion.
9 . The gang drilling machine of claim 1 , wherein the controller is further configured to:
stop the at least one of the master drills and the plurality of associated minion drills, in response to the drilling depth matching a reference plane depth.
10 . The gang drilling machine of claim 9 , wherein the controller is configured to:
determine that the drilling depth matches the reference plane depth based on the response signal matching the query signal.
11 . The gang drilling machine of claim 1 , wherein the controller is configured to:
increase the drilling depth of the at least one of the master drills and the plurality of associated minion drills, in response to the drilling depth being less than a reference plane depth.
12 . The gang drilling machine of claim 11 , wherein the controller is configured to:
determine that the drilling depth is less than the reference plane depth based on the response signal not matching the query signal.
13 . The gang drilling machine of claim 1 , wherein determining the stub length offset comprises searching a lookup table that relates the stub length time skew to the stub length offset.