FR2641932A1 - Device for evaluating the slippage between the conductive print and the holes of a multilayer printed circuit - Google Patents

Abstract

The subject of the invention is a device for evaluating the slippage between the conductive print and the holes of a multilayer printed circuit 18. This device includes two conductive holes 19, 20 passing through the circuit at the ends of which are made conductive pellets 219, 220, circular lands 120, 320 of given diameter which are made around the location of a first hole 20, and a conductive print 250; 25, 190 which connects the contours of these lands 120, 320 to the second hole 19; the device also includes means 26 for detecting a short-circuit between the two holes 19, 20. A slippage is manifested by a short-circuit between the first hole and the edge of a land, thus provoking a short-circuit between the two holes.

Description

SLIDING ASSESSMENT DEVICE
BETWEEN THE CONDUCTIVE PRINT AND THE HOLES
OF A MULTI-LAYER PRINTED CIRCUIT
The subject of the invention is a device for evaluating the slip between the conductive printing and the holes of a multilayer printed circuit.

 The realization of a multilayer printed circuit involves many steps. Inaccuracies during some of these stages can produce a shift between # of the centers of conductive pads or of savings of the conductive impression of the internal layers and the axes of the corresponding holes. Such a shift can result in particular from an out-of-tolerance realization of the conductive printing of the internal layers of the circuit, of a bad positioning of the different layers with respect to each other before they go to press, of a sliding of these layers relative to each other during their pressing, or else a sliding of the drilling of the holes for example caused by a bad positioning of the drilling drill. Such a shift results in a reduction of electrical contact in the case of the offset of a hole with respect to a conductive pad, and by a reduction in isolation in that of the decentering of a hole with respect to a savings. I1 can therefore result from an offset of this type of short circuits which risk - damaging the printed circuit. A control and an evaluation of these offsets therefore proves essential, in particular for the production of complex printed circuits, - - of large dimensions, and expensive.

 A known means for evaluating the sliding of the different layers of the printed circuit with respect to each other consists in measuring, using an appropriate graduated eyepiece, the offset between the slices of patterns produced on each of the layers of board. same time as the conductive impre3s.fJil of each of these layers and for example by means of the same material as this conductive impression. This known means is illustrated by FIGS. 1 and 2, in the particular case, taken by way of example, of a printed circuit with four layers 5, 6, 7, 8. These FIGS. 1 and 2 respectively represent a view of above and a side view of a circuit 2, provided with a protrusion 3, also called test piece, the circuit and the protrusion having been cut from a circuit 1 of larger dimensions and shown diagrammatically by dotted lines. Circuits 1 and 2 are respectively described as initial and final in the following. The test piece 3 is used to carry out tests such as for example tests relating to delamination (that is to say the lack of adhesion of the material constituting the conductive impression on the insulating support of the layers), the under-etching and the over-etching (that is to say the comparison between the real width of the tracks of the conductive impression and that expected), the metallization of the holes.

The test piece 3 can be separated from the final circuit 2 for example by breaking the narrow zone 4 separating it from this final circuit 2. More precisely, the patterns whose edges are observed with the graduated eyepiece have the shape of the letter " L "and are located at least at a predetermined corner of the test piece 3. By way of example the test piece 3 of FIGS. 1 and 2 comprises two series of patterns 9, 10, 11, 12 respectively located at two different corners: indeed for the needs of the various tests carried out on the test piece 3, the latter can be broken into several pieces intended for different users. The measurement carried out with the graduated eyepiece consists in determining the respective lengths 11, 12, 13, 14 of the edges of the ends of these "L" shaped patterns, as well as their relative offsets d2, d3.

 This known means has many drawbacks.

 First of all, its implementation is tedious.

 Then, it is imprecise because it can be distorted by an engraving or an over-engraving of the L-shaped patterns (which are similar to tracks therefore which have the same production problems).

 In addition, it is produced on the test piece 3 which may not be representative of the final circuit 2. ' To remedy this particular drawback, it is possible to provide a second test piece 30 comprising patterns 90, 100, 110, 120 similar to the patterns 9, 10, 11, 12 located on the other side of the final circuit 2 relative to the test piece. 3, as shown in FIG. 3. However, such an addition has the drawback of doubling already tedious measures and significantly increasing the cost price of the final circuit 2, this cost price depending strongly on the dimensions of the initial circuit 1 .In addition, if the surface of one of the test pieces, for example the test piece 3, is justified by carrying out tests such as those relating to delamination, over-etching and under-etching, and metallization of the holes, by countering the surface of the other test piece is not profitable by such tests.

 Consequently, this known means being implemented on the test piece 3 and not on the final circuit 2, an evaluation of the slip of the different layers of the final circuit cannot be made during the application of this circuit.

 Finally, this means does not make it possible to evaluate the sliding of the drilling of the holes, nor the offset resulting from an out of tolerance realization of the conductive impression of the internal layers of the final circuit 2, these two types of offset, in particular, do not not affecting the test piece 3 if they occur within the final circuit 2.

 The subject of the invention is a device for evaluating the slip between the conductive printing and the holes of a multilayer printed circuit which overcomes the drawbacks of the known means. To this end, the device according to the invention comprises a reference conductive hole and a main conductive hole both passing through the circuit, and at the ends C! E * s41J21S -.n; -élisees, ur the outer layers of ~ ircllt, conductive pads. This device also includes substantially circular and identical main savings, made on the inner layers of the circuit and around the location of the main hole; the edge of these savings is electrically connected to the reference hole by a conductive print. Finally, this device includes means for detecting a short circuit between the main hole and the reference hole: a slip between the conductive impression and the holes in the circuit results in a short circuit between the main hole and the edge. savings, so between the main hole and the reference hole.

 The device according to the invention is very simple to implement.

It is precise because it provides an "all or nothing" result
Being advantageously located on the final circuit, it can provide information representative of this final circuit. In addition, it can be used at any time during the application of the printed circuit, which makes it possible to control this circuit at any time.

 Finally, it takes into account all the types of offsets mentioned in the above.

The invention will be better understood on reading the following description which is made with the aid of the appended figures, these figures representing
FIG. 1, a top view of the known means,
FIG. 2, a side view of the means of FIG. 1,
FIG. 3, a top view of a variant of the means of FIG. 1,
FIG. 4, a schematic section of an embodiment of the device according to the invention,
FIG. 5, a section of an external layer of the device of FIG. 4,
- :; r ligure iv a cut of a first type of ~ cue :: 1-
internal of the device of FIG. 4,
FIG. 7, a section of a second type of internal layer of the device of FIG. 4,
- Figures 8 and 9, a first configuration of
slip corresponding to a first evaluation using the device according to the invention,
- Figures 10 and 11, a second configuration of
slip corresponding to a second evaluation using the
device according to the invention,
- Figure 12, an illustration of the link between parameters of the device according to the invention.

 In these various figures, on the one hand the real scale has not been respected, and on the other hand the same references relate to the same elements.

 Figure 4 is a schematic section of an embodiment of the device according to the invention, for assessing the slip between the conductive printing and the holes of a multilayer printed circuit, such as for example a printed circuit 18 with six layers 13, 15, 14, 16, 150, 17.

This device comprises in particular, crossing the circuit 18
- a reference conductive hole 19,
a main conductive hole 20, located at a distance dl from the reference hole,
- N = 3 secondary conductive holes 21, 22, 23 advantageously located in alignment with the holes 19 and 20 and at distances, respectively, dll, d12, d13 from the reference hole.

This device also includes conductive impressions made on each of the layers of the circuit. Cross-sections of these conductive impressions are given in FIGS. 5, 6, 7
FIG. 5 illustrates the case of the outer layers 13 and 17,
- Figure 6 illustrates the case of a mass layer or
tension, such as layers 14 and 16,
FIG. 7 illustrates the case of a logical layer,
such as layers 15 and 150.

 Finally, the device includes detection means.

a short circuit comprising for example an ohmmeter:
- between the main hole 20 and the reference hole 19,
- between each of the secondary holes 21, 22, 23 and the reference hole 19.

These means are roughly schematized and bear the reference 26.

 The conductive impressions of the outer layers 13 and 17 are substantially identical and each comprise conductive pads 219, 220, 221, 222, 223 as shown in FIG. 5. The center of the pad 219 is taken as a reference. The centers of the pads 220, 221, 222, 223 are respectively located at distances dl, d11, d12, d13 from that of the pad 219 which is substantially on the axis of the reference hole 19 and are advantageously substantially aligned so as to be arranged substantially in the same way as the holes 19, 20, 21, 22, 23. The pad 219 preferably has a different shape from the pads 220, 221, 222, 223: it is thus easy to locate. As an example, the pad 219 is square and the pads 220, 221, 222 and 223 are circular. As is known, the production of these pads 219, 220, 221, 222, 223 accompanies that of the holes 19 , 20, 21, 22, 23, respectively: these pellets prevent the etching agent of the external layers from deteriorating the metallization of the holes (the external layers being in fact produced after the assembly of the circuit and after the metallization of the holes).

 The conductive impressions of the mass or voltage layers 14 and 16 are substantially identical and each comprise sparks 120, 121, 122, 123. These spares are substantially circular. The respective centers of the savings 120, 121, 122, 123 are respectively located at the distances d1, d11, d12, d13 from the axis of the reference hole 19, and are advantageously substantially aligned so as to be arranged substantially in the same way as the holes. 20, 21, 22, 23. The respective diameters of the four savings 120, 121, 122, 123 are increasing. According to a first embodiment, the saving diameter 120 is prefixed as explained below, and the diameters Do D1, D2, D3 respectively savings 120, 121, 122, 123 form the first terms of an arithmetic sequence of prefixed reason, that is to say are such that: Dk D Dk # I = C with 1 # k. <3 where C is a prefixed constant. According to a second embodiment, it is the diameter D1 which is prefixed, and it is the diameters D1, D2, D3 which form the first terms of an arithmetic sequence of prefixed reason, while the diameter Do is simply less than the diameter D1 of a prefixed quantity.

The conductive printing of the logic layers 15 and 150 also comprises savings 320, 321, 322, 323 substantially circular, the respective centers of which are respectively located at distances d1, dll, d12, d13 from the axis of the reference hole 19 and are advantageously substantially aligned, the savings 320, 321, 322, 323 are respectively substantially identical to the savings 120, 121, 122, 123. The savings 320 and 120, 321 and 121, 322 and 122, 323 and 123 are respectively qualified as primary, secondary from a first set, secondary from a second set, and secondary from a third set. The savings of the logical layers 15 and 150 are delimited by circular contours which are connected by links 25; a link 25 also connects these contours to a conductive pad 190, for example circular, the center of which is substantially on the axis of the reference hole 19 and the diameter of which is for example substantially the same as that of the pads 20, 21, 22, 23 outer layers 13 and 17. These links 25 have for example a width substantially equal to that (standardized and correspondar> .ta 't' ie pelasse be - manufacture of printed circuits
data) of the tracks of the printed circuit tested.

The holes and conductive impressions of the
device according to the invention are produced at the same time, respectively, as the holes and the conductive impressions of the
multilayer printed circuit tested. Therefore, the device
according to the invention is subject to the same manufacturing hazards as
the circuit tested: the slip between the conductive print
and the holes of the device is therefore representative of that of the
circuit tested, especially since the device is
advantageously located on the final circuit and not on
the test tube of the initial circuit: the device is located by
example at one of the corners of the final circuit, or in its
It is also possible to set up several
devices on the same final circuit, such as for example
place four at the four corners of the circuit. Such a slip
causes an offset of the holes 20, 21, 22, 23 relative to
to the savings 120, 121, 122, 123 of the layers of mass or of
tension 14 and 16 and those 320, 321, 322, 323 of the layers
logic 15 and 150. Such a shift is likely to cause
a short circuit between one or more holes and the edges of a
or multiple savings, respectively. Such a short circuit
is detected by the ohmmeter of means 26.

To prevent such a short circuit from affecting
in the circuit tested, a savings 24 having the form of a
loop surrounds the conductive print 250 of the ground layers
or voltages 14 and 16 of the device according to the invention. As
example, this loop is rectangular.

According to the first embodiment previously
envisaged, the diameter D0 of the main savings, located at the
distance d1 from hole 19, is such that a short circuit between the
reference hole 19 and the main hole 20 corresponds to the
Maximum slip tolerated between the conductive print and the holes of the circuit under test. The determination of this maximum tolerated slip is explained in the following. A short circuit between the reference hole 19 and one of the secondary holes 21, 22, 23 corresponds to a slip which can be authorized by derogation according to the context of the application of the circuit the user of the circuit is then capable to locate the sliding of this circuit in relation to - the sliding corresponding respectively to short circuits at the level of the holes 21, 22, 23.

According to the second embodiment previously considered, it is the diameter D1 of the secondary savings of the first set, located at the distance d11 from the reference hole
19, which corresponds to the maximum tolerated slip. Diameters
D2 and D3 corresponding to slippages which may be authorized by derogation in ion form from the context of the application of the circuit. As for the diameter DO, it corresponds to a slip less than the maximum tolerated slip: if the latter is chosen as a manufacturing standard, the main hole corresponding to the diameter Do can be used to establish a classification between the cc + erent manufacturers of multilayer printed circuits.

The maximum tolerated slip is determined according to the characteristics of the holes, the conductive pads and the savings of the printed circuit tested. In practice these characteristics are standardized. For the sliding between pads and holes, we consider that at worst, the hole is tangent to the edge of the pad, which leads to the relation
GPT = 1 (DP - DMTM) - C
2 where GPT is the sliding between a pellet and a hole,
DP is the diameter of the pellet,
DMTM is the maximum diameter of the metallized hole,
C is the collar of the hole, that is to say the metallization thickness of this hole.

For the sliding between spares and holes, the distance necessary to avoid a short-circuit between the savings and the aw7 distanoe: isolation distance obviously depends on the voltage applied between this savings and this hole. We have the relationship
GET = 1 (DE - 2 DI - DMTM) - C
2 where GET is the slip between a savings and a hole,
DE is the diameter of the savings,
DI is the isolation distance,
DMTM is the maximum diameter of the metallized hole,
It is the collar of the hole.

For example, the smaller of the two values GPT and GET is chosen for the maximum tolerated slip.

From this maximum tolerated slip G, the diameter Do of the main savings is fixed in the case of the first embodiment of the invention and the diameter D1 of the secondary savings of the first set in the case of the second embodiment, using the following relation, illustrated by figure 12
D = 2 G + A where D is the diameter Do or D1 sought for savings; 2 i
A is the diameter before metallization of a standard hole 2i of the circuit tested and of the device according to the invention.

Diameters greater than D (which corresponds to Do or D1 depending on the embodiment considered) are connected to slip movements authorized by derogation in a similar manner, namely by
Dr = 2 G '+ where D' is one of the diameters greater than D sought;
G 'is the slip authorized by corresponding exemption, which can be set by the user according to the context of the application of the circuit tested.

 According to a preferred embodiment of the invention, the maximum tolerated slip is evaluated at 0.2 millimeters and corresponds to the diameter Do of the main savings. The holes have a diameter of 0.8 millimeters before metallization, which eo-.duit to a value of Do equal to D0 = 2 x 0.2 + 0.8 = 1.2 millimeters.

the diameters D1, D2, D3 are defined by:
Dk - Dk-1 = 0.1 millimeters where 1 <k <3, i.e.
D1 = 1.3 millimeters,
D2 = 1.4 millimeters,
D3 = 1.5 millimeters.

the corresponding overrides are given by
G1 = 1 (1.3 - 0.8) = 0.25 millimeters,
2
G2 = 1 (1.4 - 0.8) = 0.30 millimeters,
2
G3 = 1 (1.5 - 0.8) = 0.35 millimeters.

2
Advantageously, the circuit tested comprises a plurality of devices according to the invention. By way of example, this circuit comprises four devices of this type respectively located at its four corners.

 Figures 8 and 9 show a first sliding configuration corresponding to the case where there is a short circuit between the reference hole 19 and the main hole 20, and where there is no short circuit between the reference 19 and the secondary holes 21, 22, 23. It is deduced from the preceding values that the real slip in the circuit tested is between 0.20 millimeters and 0.25 millimeters.

 More specifically, FIG. 8 represents two pads 26 and 27, between which two tracks 28 and 29 pass: this configuration corresponds to class four for manufacturing printed circuits, known per se by those skilled in the art (the respective centers of the pads 26 and 27 are separated by a standardized distance a and equal to 2.54 millimeters) .The offset of the hole 31 relative to the patch 27 is such that the trace of this hole overflows from the patch 27, which reduces the isolation . between this pad and this hole on the one hand and the track 29 on the other hand the distance 1 @, characteristic of class four, which separates the pad 26 from the track 28 is greater than that 12 between the edge of the hole 31 and track 29 with a value 13 at most substantially equal to 0.05 millimeters.

In FIG. 9, the isolation distance 14 between the hole 32 and the savings 33 is reduced by at most substantially 0.05 millimeters compared to that corresponding to the maximum tolerated slip.
Figures 10 and 11 are respectively similar to Figures 8 and 9 except that they correspond to the case where there is a short circuit between the reference hole 19 and the main hole 20, as well as between this reference hole 19 and the first secondary hole 21, while there is no short-circuit between the reference hole 19 and the secondary holes 22, 23: according to the previous values, the real slip in the circuit tested is between 0.25 millimeters and 0.30 millimeters. Consequently, the distance 1'2 in FIG. 10 between the edge of the hole 31 and the track 29 is shorter than that 12 in FIG. 8 (the value 1'3, analogous to 13, being substantially between 0.05 millimeters and 0.10 millimeters). Likewise, the isolation distance 1'4 of FIG. 11 is reduced by a value appreciably between 0.05 millimeters and 0.10 millimeters compared to that corresponding to the maximum tolerated slip.

 Of course, the invention is not limited to the embodiments described in the foregoing. In particular, a device comprising non-aligned conductive holes, and spaced in any way falls within the scope of the invention.

Claims (9)

 1. Device for evaluating the slip between the conductive print and the holes of a multilayer printed circuit (18), characterized in that it comprises  - a reference conductive hole (19) passing through the circuit (18),  - a main conductive hole (20) passing through the circuit (18),  - conductive pads (219, 220) produced on the external layers (13, 17) of the circuit (18) at the ends of the reference hole (19) and the main hole (20),  - a set of main savings (120; 320) substantially circular, substantially of the same predetermined diameter (du), produced on the internal layers (14, zig; 15, 150) of the circuit (18) around the location of the hole main (20),  - a conductive print (250; 25, 190) connecting the contours of the main savings (120; 320) to the reference hole (19),  - Means for detecting a short circuit (26) between the main hole (20) and the reference hole (19).  2. Device according to claim 1, characterized in that it further comprises  - N secondary conductive holes - (21, 22, 23) passing through the circuit (18),  - conductive pads (221, 222, 223) produced on the external layers (13, 17) of the circuit (18) at the ends of the secondary holes (21, 22, 23),  - N sets of secondary savings (121, 122, 123 321, 322, 323) substantially circular, formed on the internal layers (14, 16 ~ 15, 150) of the circuit (18) respectively around the locations of the N secondary holes  (21, 22, 23), the secondary savings of a given set having substantially the same diameter (D1; D2 ;; D3), the diameters of the secondary savings of the successive sets increasing and being greater than the diameter (D0) of the main savings ,  - a conductive print (250; 25, 190) connecting the contours of the secondary savings to the reference hole (19),  - means for detecting a short circuit (26) between each of the secondary holes (21; 22; 23) and the reference hole (19).  3. Device according to claim 2 characterized in that the diameter (Do) of the main savings followed by the diameters (D1, D2, D3) of the secondary savings of the successive sets form the first terms of an arithmetic sequence of prefixed reason.  4. Device according to claim 2, characterized in that the diameters (D1, D2, D3) of the secondary savings of the successive sets form the first terms of an arithmetic sequence of prefixed reason.  5. Device according to one of the preceding claims, characterized in that it further comprises isolation means (24) between the conductive print (250) delimiting the contours of the main and secondary savings and the conductive elements of the circuit tested.  6. Device according to one of the preceding claims, characterized in that the reference hole (19) the main hole (20), and the secondary holes (21, 22, 23) are substantially aligned.  7. mullicouehes printed circuit, characterized in that it comprises a device according to one of the preceding claims, located at one of these corners.  8. Multilayer printed circuit, characterized in that it comprises a device according to one of claims 1 to 6, located substantially in its center.  9. Multilayer printed circuit, characterized in that it comprises four devices according to one of claims 1 to 6, respectively located at its four corners.