Method for the recognition of testing errors in the test of microwirings

Method for the recognition of testing errors in a test of microwirings. The method for the recognition of testing errors in the test is used in particular in an electron beam test of microwirings in the form of a printed circuit board (LP) having a plurality of networks (NW1 . . . NW9). Every network has a plurality of contact points (1 . . . 24). Interruptions (U) in networks (NW 2) and shorts (K1, K2) between networks (NW1 . . . NW3) of a test group (TG1) or, respectively, shorts (K3) between networks (NW2, NW4) of different test groups (TG1, TG2), that are found in a respective main test, are confirmed in a respective follow-up test or testing errors that arose in the main test, for example due to microfields or surface contaminations, are identified.

BACKGROUND OF THE INVENTION 
The present invention is directed to methods for recognizing testing errors 
in a test, particularly an electron beam test of microwirings in the form 
of printed circuit boards having a plurality of networks. 
In the prior art European Application EP 0 189 777 B1 discloses testing 
methods that can supply incorrect test results, for example due to 
existing microfields or surface contaminations on the printed circuit 
board to be tested. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide improved methods that 
enable a distinction to be made between testing errors and true errors 
(interruptions, shorts) of a printed circuit board by means of additional 
intermediate tests or follow-up tests. This object is achieved by the 
following methods of the present invention. 
One method of the present invention involves identifying interruptions in 
the networks of a printed circuit board. The method is for recognizing 
testing errors in a test, particularly an electron beam test of 
microwirings in the form of a printed circuit board having a plurality of 
networks. Every network has a plurality of contact points, wherein 
interruptions in the networks are identified. All contact points have a 
zero potential before the beginning of a main test. A network not yet 
intentionally charged is respectively charged to a charging potential 
differing from the zero potential in a first step of the main test via a 
contact point of the respective network. Respective potentials of contact 
points not intentionally charged in the respective network are measured in 
a second step of the main test. An interruption in the respective network 
is found in a third step of the main test in that an interruption contact 
point of the respective network was not charged to the charging potential 
via a line of the respective network. This method of the present invention 
is a follow-up test to the main test and has the following steps. The 
respective interruption contact point is intentionally charged to the 
charging potential in a first step of the follow-up test. Potentials of 
contact points not intentionally charged in the follow-up test in the 
respective network are measured in a second step of the follow-up test. A 
respective interruption found in a third step of the main test is 
confirmed in a third step of the follow-up test when at least one contact 
point of the respective network was not charged to the charging potential 
via a line of the respective network. A testing error that arose in the 
main test is respectively found when the respective interruption found in 
the third step of the main test is not confirmed. 
Another method of the present invention involves identifying shorts between 
networks of the printed circuit board. All contact points have a zero 
potential before the beginning of the main test. A respective network not 
yet intentionally charged is intentionally charged to a charging potential 
differing from the zero potential in a first step of the main test via at 
least one contact point of the respective network. The potentials of other 
networks not yet intentionally charged are measured via at least one 
contact point of the respective, other network in a second step of the 
main test. A respective short from one of the networks already 
intentionally charged to a respective, other network not yet intentionally 
charged is found in a third step of the main test in that at least one 
short-circuit contact point of the respective, other network not yet 
intentionally charged was charged to the charging potential via the 
respective short. This method of the present invention is a follow-up test 
to the main test and has the following steps. All contact points are 
discharged before the follow-up test. The network of the respective 
short-circuit contact point is intentionally charged to the charging 
potential in a first step of the follow-up test. Potentials of networks 
not yet intentionally charged in the follow-up test are identified in a 
second step of the follow-up test in that the potential is respectively 
measured via at least one contact point of the respective network not yet 
intentionally charged in the follow-up test. A respective short found in a 
third step of the main test is confirmed in a third step of the follow-up 
test when a network not yet intentionally charged in the follow-up test 
was charged to the charging potential via the respective short. A testing 
error that occurred in the main test is respectively found when the 
respective short found in a third step of the main test is not confirmed. 
A further method of the present invention involves identifying both 
interruptions and shorts in the printed circuit board. All contact points 
have a zero potential before the beginning of the main test. A network 
respectively not yet intentionally charged is intentionally charged to a 
charging potential differing from the zero potential in a first step of 
the main test via a contact point of the respective network. Respective 
potentials of contact points not intentionally charged in the respective 
network are measured in a second step of the main test. An interruption in 
the respective network is identified in a third step of the main test in 
that an interruption contact point of the respective network was not 
charged to the charging potential via a line of the respective network. 
The potentials of other networks not yet intentionally charged are 
respectively measured in a fourth step of the main test via at least one 
contact point of the respective, other network. A respective short from 
one of the networks already intentionally charged to the charging 
potential to a respective, other network not yet intentionally charged is 
identified in a fifth step of the main test in that at least one 
short-circuit contact point of the respective, other network not yet 
intentionally charged was already charged to the charging potential via 
the respective short. All contact points of the printed circuit board are 
discharged before the follow-up test. The network of the respective 
short-circuit contact point is intentionally charged to the charging 
potential via a respective short-circuit contact point in a first step of 
the follow-up test. Potentials of other networks not yet intentionally 
charged in the follow-up test are identified in a second step of the 
follow-up test in that the potential is respectively measured via at least 
one contact point of the respective, other network not yet intentionally 
charged in the follow-up test. A respective short found in a fifth step of 
the main test is confirmed in a third step of the follow-up test and a 
respective, other network that has no been intentionally charged and 
participates in the respective short is unambiguously identified and 
reported together with the network of the respective short-circuit contact 
point when the network not yet intentionally charged in the follow-up test 
was charged to the charging potential via the respective short. A testing 
error that occurred in the main test is respectively identified when the 
respective short identified in the fifth step of the main test is not 
confirmed. 
In yet a further method of the present invention for identifying 
interruptions and shorts in the printed circuit board the majority of 
networks are combined to form at least one test group and the main test is 
respectively implemented for one test group and is supplemented by a 
respective intermediate test. 
Networks within the respective test group that have again already 
discharged due to a fault are identified in the intermediate test in that 
the potential of at least one contact point of a respective network is 
respectively measured and is found whether or not the potential 
corresponds to the charging potential. All contact points are discharged 
before a follow-up test. A respective network identified in the 
intermediate test is intentionally charged to the charging potential in a 
first step of the follow-up test. Potentials of other networks of the 
respective test group are measured via at least one respective contact 
point in a second step of the follow-up test. A short is identified in a 
third step of the follow-up test and a respective, other network 
participating in the short is unambiguously identified and is reported 
together with the respective network intentionally charged in the first 
step of the follow-up test and likewise participating in the short when 
the network not yet intentionally charged in the follow-up test was 
charged to the charging potential via the short. 
The respective potentials of networks of other test groups are measured via 
at least one contact point and of the respective network of the other test 
group in a first step of a respective intermediate test. A respective 
short that overlaps the test groups from one of the networks of the 
respective test group that were already intentionally charged in the 
respective main test to a respective network of the other test group is 
identified in a second step of the respective intermediate test in that at 
least one short-circuit contact point overlapping the test groups in the 
respective network of the other test group was already charged to the 
charging potential via the respective short overlapping the test groups. 
Furthermore, all contact points of the printed circuit board are discharged 
as a third step of a respective intermediate test. The network of the 
respective short-circuit contact point that overlaps the test groups is 
intentionally charged to the charging potential in a first step of a 
follow-up test and via a short-circuit contact point that overlaps the 
test groups. Potentials of networks over a respective, other test group 
that were not yet intentionally charged in the follow-up test are 
identified in a second step of the follow-up test in that the respective 
potential is measured via at least one contact point of the respective 
network not yet intentionally charged in the follow-up test in the 
respective, other test group. A respective short that overlaps the test 
groups and was found in a second step of the intermediate test is 
confirmed in a third step of the follow-up test when a network not yet 
intentionally charged in the follow-up test in the respective, other test 
group was charged to the charging potential via the respective short that 
overlaps the test groups. A testing error is found when the short 
identified in a third step of the main test is not confirmed. 
An advantage of the present invention is that more reliable test results 
can be achieved than in the afore-mentioned, prior art methods by the 
methods of the present invention with relatively few additional tests 
(intermediate test, follow-up test).

DESCRIPTION OF THE PREFERRED EMBODIMENT 
For illustrating the methods of the present invention, the single FIGURE 
depicts a printed circuit board LP on whose surface are located networks 
NW1 . . . NW9 that are insulated from one another. The networks NW1 . . . 
NW3 are combined to form a test group TG1, the networks NW4 . . . NW6 are 
combined to form a test group TG2 and the networks NW7 . . . NW9 are 
combined to form a test group TG3. Each of the networks NW1 . . . NW9 has 
a plurality of contact points 1 . . . 24, whereby the network NWl has the 
contact points 1, 2 and 3, the network NW2 has the contact points 4, 5 and 
6, the network NW3 has the contact points 7, 8 and 9, the network NW4 has 
the contact points 10 and 11, the network NW5 has the contact points 12, 
13 and 14, the network NW6 has the contact points 15 and 16, the network 
NW7 has the contact points 17, 18 and 19, the network NW8 has the contact 
points 20 and 21 and the network NW9 has the contact points 22, 23 and 24. 
The networks NW1 . . . NW9 are symbolically indicated by parallel pairs of 
lines that cross at a right angle and a line of the network is referenced 
L in the network NW2. The line L has an interruption U that separates the 
contact point 6 from the remaining network NW2. The network NW2 is 
connected to the network NW3 via a short K1, to the network NW1 via a 
short K2 and to the network NW4 via a short K3 that overlaps test groups 
TG1 and TG2. 
For charging a network, for example, a primary electron beam is directed 
onto a contact point of the network. Another possibility for charging the 
network is, for example, by using ion irradiation, by generating 
photoelectrons with laser emission or by using microelectrodes. For 
measuring potentials at contact points, a respective primary electron beam 
that is usually also used for charging is directed onto the respective 
contact point and a secondary electron beam is thereby generated. For 
measuring the potentials at the contact points, the secondary electron 
current that proceeds into a detector is evaluated with an opposing field. 
Negatively charged contact points accelerate the emitted secondary 
electrons that can thereby overcome the opposing field. Thus, a high, 
detected current results therefrom as does a high signal for charged 
contact points, whereas a low current and, thus, a low signal results from 
uncharged contact points. The measurement of the potentials at the contact 
points can also occur, for example, via microelectrodes. By way of 
example, the drawing shows a primary electron beam PE1 directed onto the 
contact point 4 for the purpose of charging the network NW2. A primary 
electron beam PE2 directed onto the contact point 5 generates secondary 
electrons SE2; a primary electron beam PE3 directed onto the contact point 
6 generates secondary electrons SE3; a primary electron beam PE5 directed 
onto the contact point 7 generates secondary electrons SE5; a primary 
electron beam PE6 directed onto the contact point 10 generates secondary 
electrons SE6; and a primary electron beam PE7 directed onto the contact 
point 17 generates secondary electrons SE7 via which the potentials of the 
appertaining contact points are respectively identified. When it is 
assumed that all contact points before a test have a potential of zero, 
then the first step of a main test for identified interruptions in the 
networks begins in that a network that has not yet been intentionally 
charged, for example the network NW2, is intentionally charged to a 
charging potential differing from zero potential via a contact point of 
the respective network, for example the contact point 4. The expressions 
"zero potential" and "charging potential" are to be interpreted as ranges 
of potential, whereby the ranges of potential do not mutually overlap. In 
a second step of the main test for identifying interruptions in networks, 
potentials of contact points that are not intentionally charged in the 
respective network, for example the contact points 5 and 6 of the network 
NW2, are respectively measured. In a third step of the main test for 
identifying an interruption in a network, the respective interruption is 
identified in that an interruption contact point of the respective network 
has not been charged to the charging potential via a line, for example the 
contact point 6 via the line L of the respective network. Secondary 
electrons can be influenced such by microfields and/or surface 
contaminations such that an interruption is only simulated. 
In order to avoid these testing errors, a first, inventive follow-up test 
is undertaken after the main test. Before a first follow-up test of the 
present invention, all contact points 1 . . . 24 of the printed circuit 
board LP are thereby discharged. The discharging here and in what follows 
can occur by means of a low-energy, positive ion beam when the contact 
points had been negatively charged. In the first follow-up test of the 
present invention a respective interruption contact point, for example the 
contact point 6, is intentionally charged to the charging potential in a 
first step. Potentials of contact points that were not intentionally 
charged in this follow-up test, for example the contact points 4 or, 
respectively, 5 of the respective network NW2, are measured in a second 
step. In a third step of the first follow-up test of the present 
invention, the respective interrupts identified in the main test are 
confirmed when at least one contact point (the two contact points 4 and 5 
in the single FIGURE) is not charged to the charging potential via a line 
of the respective network proceeding from the network of the respective 
interruption contact point, here the network NW2 having the interruption 
contact point 6. If, for example, the interruption contact point 6 had 
been identified in the main test and yet an interruption U was not 
present, then, for example, the contact points 4 and 5 would have been 
charged by the network NW2 to the charging potential and a testing error 
that occurred in the main test would have been identified. 
In a test for identifying shorts between networks and given the assumption 
that all contact points nave the zero potential before the beginning of a 
main test, a network, for example the network NW2, that has not yet been 
intentionally charged is intentionally charged to a charging potential 
different from the zero potential via at least one contact point, for 
example the contact point 4, in a first step of the main test. In the 
second step of the main test, respective potentials from other networks, 
for example the network NW3, that have nor yet been intentionally charged 
are measured via at least one contact point, for example the contact point 
7, of the other network NW3. In a third step of the main test, a 
respective short, for example the short K1 from one of the networks 
already intentionally charged, for example NW1 and NW2, to another network 
that has not yet been intentionally charged, for example the network NW3, 
is identified in that at least one short-circuit contact point, for 
example the contact point 7, of the other network not yet intentionally 
charged was already charged to the charging potential via the respective 
short-circuit. When measuring potentials of the contact points of a 
network, a charged network and, thus, a shirt, for example a short K1 due 
to the network NW3, can be likewise simulated, for example by microfields 
and surface contaminations 
In order to avoid these testing errors, a second follow-up test of the 
present invention is provided wherein the network, for example the network 
NW3, of the respective short-circuit contact point is intentionally 
charged to the charging potential via a respective short-circuit contact 
point, for example the contact point 7, in a first step after all contact 
points 1 . . . 24 have been discharged. In a second step, potentials of 
networks, for example the networks NWl and NW2, not yet intentionally 
charged in this follow-up test are identified in that the potential of the 
network not yet intentionally charged in the follow-up test is 
respectively measured via at least one contact point, for example the 
contact point 2 or the contact point 5. In a third step of the second 
follow-up test of the present invention, the respective short, for example 
the short K1, found in the third step of the main test is confirmed when a 
network, for example the network NW2, not yet intentionally charged in the 
follow-up test was charged to the charging potential via the respective 
short. Without the short K1 for example, the networks NW1 and NW2 would 
not have been charged in this case and the short found in the main test 
would have been reported as being only due to a testing error. 
The tests for identifying interruptions in networks and shorts between 
networks can be combined in such a way that a network is respectively 
successively charged in order to find an interruption inside the 
respective network and that, subsequently, networks not yet intentionally 
charged are measured in order to find shorts between one of the networks 
already charged and the respective network. When, for example, the 
networks NW1 and NW2 were already intentionally charged in the main test, 
then, for example, the network NW3 (insofar as it is charged but was not 
intentionally charged) could have been charged due to a short to the 
network NW1 and/or a short to the network NW2. An identification of the 
networks participating in the respective short is thus not possible 
without ambiguity. The shorts K2 and K3 provided in the drawing thereby 
have no significance. 
A main test for finding interruptions in networks and shorts between 
networks can be followed by a third follow-up test of the present 
invention wherein all contact points 1 . . . 24 of the printed circuit 
board LP are initially discharge. In a first step the network of the 
respective short-circuit contact point, for example the network NW3, is 
intentionally charged to the charging potential via a respective 
short-circuit contact point, for example via the contact point 7. 
Potentials of other networks, for example the networks NW1 and NW2, not 
yet intentionally charged in the follow-up test are identified in a second 
step of the follow-up test in that the respective potential of the 
respective, other network not yet intentionally charged in the follow-up 
test is measured via at least one contact point, for example the contact 
point 2 or the contact point 5. In a third step of the third follow-up 
test of the present invention, a respective short for example the short 
K1, found in a fifth step of the main test is confirmed and a respective, 
other network that has not yet been intentionally charged and participates 
in the respective short, for example the network NW2, is unambiguously 
found and reported together with the network of the respective 
short-circuit contact point, for example the contact point 7, when the 
network not intentionally charged in the follow-up test was charged to the 
charging potential via the respective short. An unambiguous allocation of 
the networks participating in the respective short is thus possible on the 
basis of this follow-up test even though intentionally charged networks 
are not respectively intentionally discharged before the intentional 
charging of another network but remain charged. As was already the case in 
the second follow-up test of the present invention, testing errors due, 
for example, to microfields and/or surface contaminations can be 
correspondingly distinguished from true printed circuit board faults such 
as, for example, interruptions and shorts. 
Since networks already intentionally charged can have a disrupting 
influence on a measurement of the potential of another network and the 
networks (due to a limited insulatability of the printed circuit board) 
remain charged for only a limited time, networks to be tested must be 
combined to form test groups, particularly for larger printed circuit 
boards. Since only all networks of one test group are maximally charged at 
the same time, a plurality of discharging steps, for example, and 
additional steps for identifying shorts between test groups are required 
and denote additional outlay. For this reason, a test group cannot be 
arbitrarily small. It can occur under certain circumstances beginning with 
a certain size of the test group that a discharge of the network occurs 
before a test group is completely tested due to faults, for example due to 
inadequate insulation capability of the printed circuit board or charge 
clouds over the respective network. When it is assumed that only the short 
K2 is present between the networks NW1 and NW2 and the network NW1 is 
intentionally charged at the beginning of a main test of the test group 
TG1, then the network NW1 can already have been again discharged again 
when, for example, the potential of the network NW2 is measured for 
finding a short. The network NW1 can thus no longer charge the network NW2 
via the short K2, as a result whereof the short K2 remains undetected in 
the main test. In order to avoid this testing error, an intermediate test 
of the present invention can be provided between the main tests and its 
following follow-up test after the main test for finding interruptions in 
networks and shorts between networks. In the intermediate test of the 
present invention, networks such as, for example, the network NW1 that 
have already again discharged are found within the respective test group 
TG1 in that the potential of at least one contact point of a respective 
network, for example the contact point 2 of the network NW1, is 
respectively measured and whether or not the potential corresponds to the 
charging potential is found. A respective follow-up test is implemented 
for the uncharged networks found in the intermediate test that were not 
suitable for finding shorts, this follow-up test being such that the third 
follow-up test of the present invention is implemented, whereby the 
networks identified in the preceding intermediate test of the present 
invention are subjected to this follow-up test instead of the networks 
having the short-circuit contact points or in addition to the networks 
having the short-circuit contact points. For example, the network NW1 
found in the intermediate test is thus intentionally charged and the short 
K2 to the network NW2 is identified, even though the network NW1 was 
already discharged in the main test. 
When a plurality of test groups are formed, then shorts can occur between 
networks of different test groups that overlap test groups such as, for 
example, the short K3 between the networks NW2 and NW4 overlapping the 
test groups. In a further intermediate test of the present invention, the 
respective potentials of networks of other test groups, for example of the 
networks NW4 . . . NW9 of the test groups TG2 and TG3, are measured via at 
least one contact point of the respective network of the other test group, 
for example the contact point 10 of the network NW4 of the test group TG2. 
In a second step of the respective, further intermediate test, a 
respective short overlapping test groups from one of the networks of the 
respective test group already intentionally charged in the respective main 
test to a respective network of the other test group is found in that at 
least one short-circuit contact point overlapping the test groups in the 
respective network of the other test group was already charged to the 
charging potential via the respective short overlapping the test groups. 
The short K3 that overlaps test groups for example, is found in that, for 
example, at least the short-circuit contact point 10 of the network NW4 of 
the test group TG2 was already charged to the charging potential via the 
short K3 overlapping the test groups. 
When at least one short-circuit contact point overlapping test groups or, 
respectively, one short overlapping test groups, for example the 
short-circuit contact point 10 and the short K3, were found in the further 
intermediate test of the present invention, then all contact points 1...24 
of the printed circuit board can be inventively discharged as a third step 
of the respective intermediate test before a follow-up test of the present 
invention is also implemented in this case in order to potentially confirm 
a short or find a testing error. In this follow-up test of the present 
invention, the network NW2 is intentionally charged to the charging 
potential via, for example the short-circuit contact point 10 overlapping 
test groups in a first step. In a second step, potentials of networks NW1 
. . . NW3 and NW7 . . . NW9 of the test groups TG1 and TG3 that have not 
yet been intentionally charged in the follow-up test are found in that the 
respective potential is measured via at least one contact point 2, 4, 7, 
17, 20 and 22. In a third step, a respective short K3 overlapping test 
groups and found in a second step of the further intermediate test of the 
present invention is confirmed when a network of the respective, other 
test group, for example the network NW2 of the test group TG1, that was 
not yet intentionally charged in the follow-up test was charged to the 
charging potential via the respective short K3 that overlaps the test 
groups. If the short K3 that overlaps the test groups is not confirmed in 
the follow-up test of the present invention, a testing error is present. 
The invention is not limited to the particular details of the method 
depicted and other modifications and applications are contemplated. 
Certain other changes may be made in the above described method without 
departing from the true spirit and scope of the invention herein involved. 
It is intended, therefore, that the subject matter in the above depiction 
shall be interpreted as illustrative and not in a limiting sense.