EP3685640A1

EP3685640A1 - Printed circuit board having a solder stop layer and method for coating a printed circuit board with a solder stop layer at least in some regions

Info

Publication number: EP3685640A1
Application number: EP18778408.7A
Authority: EP
Inventors: Eberhard Heiser
Original assignee: Fela GmbH
Current assignee: Psl Holding GmbH
Priority date: 2017-09-19
Filing date: 2018-09-18
Publication date: 2020-07-29
Also published as: DE102017121726A1; WO2019057733A1

Abstract

The invention relates to a printed circuit board (1, 6), which has a surface (2, 7) and at least one electrical contact (3, 8), which protrudes from the surface of the printed circuit board in the direction perpendicular to the surface of the printed circuit board, wherein the electrical contact is designed as a solder pad (3) having a contact surface (3a) for electrical contacting against said direction or as a conducting track (8), and the surface of the printed circuit board is covered with a solder stop layer (4, 5, 9) at least in some regions such that a solder stop barrier (4, 5) for the at least one electrical contact protruding from the surface of the printed circuit board is formed if said electrical contact is designed as a solder pad and/or such that an insulation layer (9) that electrically insulates portions of the conducting track that protrude from the surface of the printed circuit board is formed by the solder stop layer if the electrical contact is designed as a conducting track, the solder stop layer consisting of a cured solder stop ink and being designed in such a way that the solder stop barrier has a curved surface (4a, 5a) at least in some regions, which surface has the shape of a meniscus surface or drop surface, and/or that the greatest thickness (D) of the electrically insulating insulation layer in the direction perpendicular to the surface of the conducting track facing away from the printed circuit board is less than 125% of the thickness (d) of the electrically insulating insulation layer at the edges of the surface of the conducting track facing away from the surface of the printed circuit board in the direction parallel to the surface of the conducting track and perpendicular to the edge in question. The invention further relates to a method for producing such a printed circuit board .

Description

The invention relates to a printed circuit board with a Löststopp- layer with the features of the preamble of claim 1 and a method for at least partially Beschich ^¬ tion of a printed circuit board with a Lötstoppschicht with the features of Preamble of claim 8.

Printed circuit boards are usually coated according to current practice with a Lötstopplack, wherein the electrical Kontak ^¬ te the circuit board are excluded from the solder resist. By this measure, the circuit board can be protected from corrosion and mechanical damage, their Durchschlagfestig ^¬ speed can be increased and with reduced solder consumption, the formation of solder bridges can be avoided.

A hitherto usual procedure when this coating is to coat the entire surface of the printed circuit board with egg ^¬ nem photosensitive solder resist and then to make locally removable by selective exposure using a film or mask the solder resist, so that the contacts can be exposed, for example, by using suitable chemicals. But this has several disadvantages.

First, it comes even with careful process control repeatedly to the fact that an offset is ent ^¬ the exposure process, which is why the mask layer must be wider than the structure to be exposed. Thus, due to the production process, a gap arises between the protective lacquer layer and the contact, in which, in addition, deposition of residual chemicals may occur. Furthermore, in this way substantially Lötstopplackschichten with all places of the PCB surface on which the

Layer is not removed, the same thickness can be realized, so no adaptation of Lötstopplackschichten to locally benö ^¬ tigte dielectric strength or in the subsequent processing process locally desired supporting layer thicknesses vorgenom ^¬ men.

Another already known possibility of applying solder resist ^layers to printed circuit boards is screen printing. Even with this approach play masks, which cover the contacts are not to be coated, one we ^¬ sentliche role. Accordingly, an unwanted ^¬ wünschter offset is also here, and a flush finish to contacts or conductors can not be achieved. Furthermore, no adaptation of the solder resist ^layers to locally required dielectric strength or, in the further processing, locally desired supporting layer ^thicknesses can also be carried out by screen printing. The object of the invention is to at least provide an Improvement ^¬ te sections with a solder resist beschich ^¬ preparing printed circuit board and an improved method for at least in sections coating printed circuit boards with a solder barrier ^¬ paint which avoids these disadvantages.

This object is achieved by a printed circuit board with solder ^¬ stop layer with the features of claim 1 and a method for at least partially coating with the features of claim 9. Advantageous developments of the invention are the subject of the dependent claims.

The printed circuit board according to the invention has a surface and at least one electrical contact which is lowered in the direction of right to the surface of the circuit board protrudes beyond the surface of the circuit board, on.

The electrical contact may be designed as a soldering pad with a contact surface for electrical contacting opposite to this direction or designed as a conductor track. If more electrical contacts are present, they of course do not necessarily have all the solder pad or all be configured as a conductor track, but they can of course also be partly partially as Head ^¬ ground as solder pad and.

In this case, the surface of the circuit board is at least from ^{¬ section} covered with a Lötstoppschicht, so that a solder-stop barrier for the at least one electrical Kon ^¬ tact, which projects beyond the surface of the circuit board, ge ^¬ forms, if this is designed as a solder pad and / or so that an electrically insulating insulating layer projecting beyond the surface of the conductor track is formed by the solder stop layer when the electrical ^{contact is} configured as a conductor track.

The invention is characterized in that the solder stop barrier is composed of a cured Lötstopptinte and that the solder resist barrier at least partially has a curved surface having the shape of a meniscus surface or drops upper ^¬ surface and / or that the largest thickness of the electrically iso ^¬ lierenden insulating layer in Direction perpendicular to the side facing away from the circuit board surface of the conductor track is less than twice as thick as the thickness of the electrically insulating ^¬ insulating layer at the edges of the surface facing away from the surface of the circuit board surface of the conductor in Direction parallel to the surface of the track and perpendicular to its edges.

Because the solder resist stopping ink by a cured solder is realized, ie by a solder resist, which is initially a liquid compared to Löstopp paints ^¬ considerably lower viscosity possible ^¬ ness is created, a much more focused modeling of solder ^¬ stop layers to achieve, for example, by using the physics of liquid interfaces for targeted Modellie ^¬ tion of Lötstoppschichten, which are then cured, for example ^¬ by irradiation with light of a certain Wel ^¬ lenlänge, in particular with UV light and / or by heat treatment ^¬ treatment , Such solder resists are, for example, from Taiyo Ink MFG. Co. Ltd or Agfa Materials available.

It is essential for Lötstoppschichten of conductor tracks, that the greatest thickness of the electrically insulating insulation ^¬ layer in the direction perpendicular to the off from the circuit board facing surface of the conductor track less than 125% of the thickness of the electrically insulating insulation layer at the edge of the surface of the PCB facing surface of the conductor in the direction parallel to the surface of the conductor and perpendicular to the edge is designed. In this way, much can material more efficiently than previously ensured ^¬ to that desired for a given circuit board

Thickness is present in all directions. It is particularly preferred if these thicknesses are approximately equal. It is essential for solder stop layers on soldering pads that the curved surfaces predetermined by the liquid boundary surface, ie meniscus surfaces, which, for example, interact with an edge of the electrical capacitor. Takts, ie a contact surface with the surface of the circuit board connecting side surface of the electrical Kon ^¬ clock can be generated or drop surfaces, in particular ^¬ then when such a side surface is not available, can be obtained.

By appropriate selection of parameters can be generated, which is preferable especially when it is desired that also Lot comes to the edge of the electric contact in contacting the contact surface with this approach as Her ^¬ convex meniscus surfaces or Tropfenoberflä ^¬ chen. On the other hand, read ^¬ sen, however, also create concave meniscus surface in this way, which are particularly suited to one to ensure high throughput ^¬ dielectric strength at the edges of the electrical contact without, as was previously the case, the entire area of the surface a must be applied to the maximum Anforderun ^¬ gen to the dielectric strength sufficient LöstStoppschicht. Conversely, it is, in particular through the use of Kapillaref ^¬ fekten also possible to ensure that the solder resist barrier contacts an edge of the at least one electrical Kon ^¬ clock and / or even continuously and überlappfrei adjoins the contact area.

Another degree of freedom in modeling the solder ^¬ stop barrier and / or the electrical insulation layer can be won by structuring the edges of the at least one electrical contact, for example, undercut or deviating extend at an angle from a surface Norma ^¬ len the surface of the printed circuit board leaves. In this way, even in situations where a wetting angle is fixed, the geometry of the generated curved meniscus surface are selectively influenced.

In particular, the solder resist or solder stop barrier may be the first time such a mo ^¬ delliert by applying the teaching of the invention that different at different points of the solder ^¬ stop layer on the same board

Thicknesses and / or supporting layer thicknesses are rea ^¬ lisiert. For example, a concave meniscus with a continuously variable and überlappfreien connection to the electrical conductor at the edge thereof ^¬ rule a higher dielectric strength than riding be ^¬ where the breakdown strength is also not needed in the laterally displaced from the conductor portion. According to a particularly preferred embodiment, the Lei ^¬ terplatte a solder stop barrier having a substantially planar portion and the thickness of the solder stop barrier in this substantially planar portion of the thickness of a substantially planar portion of the meniscus surface, the shape of the curved Section pretends deviates. To this

Manner that the subsequent modification of the ^¬ cured solder resist layer produced in a first step and at least partially out can be practically realized in particular by a differentiated tielles printing, for example, can in WAIVED portions also specifically the thickness of the solder resist layer ^¬ influenced and thus, for example, be adapted to a dielectric strength required for a given application.

The inventive method for at least partially coating such a printed circuit board, which has a surface and at least one electrical contact, which protrudes in the direction perpendicular to the surface of the printed circuit board over the surface of the printed circuit board with a LötStoppschicht- net is characterized in that the solder resist layer is applied as a solder resist ink ^¬ and cured.

It is particularly advantageous, if the Lötstopptinte is applied with egg nem inkjet printer, because thereby the notwen ^¬ ended positioning accuracy without the use of masks is sufficient he ^¬.

An equally advantageous alternative to this is that the solder stop ink is applied in a 3D printing process. One difference between these two methods can be made un ^¬ ter alia, in that the curing step is made to be ^¬ different points in time.

Thus, when applied with an inkjet method, a plurality of drops of the Lötstopptinte can only be applied to the surface of the circuit board and then the thus generated flues ^¬ sigkeitsmenge be cured, so that the surface of a larger area of the resulting solder resist layer or solder ^¬ stop barrier is influenced by the interfacial physics of this solder stop ink reservoir.

When using a 3D printing process can provide, however, that Lötstopptintentröpfchen or groups of solder stop ^¬ ink droplets are cured and then further Lötstopptintentröpfchen be applied to the already applied and been cured ^¬ Lötstopptintentröpfchen. This creates a greater freedom in terms of targeted Mo ^¬ model- ling of the solder resist barrier, but can bring a waiver of larger areas with curved meniscus surfaces with it.

It may be particularly advantageous that, prior to the application of the soldering ink, the flanks of the at least one electrical contact can be structured at least in sections, that is, for example, be undercut, bevelled or otherwise deformed ver ^¬ , as in this way the surface interaction with the solder stop ink can be selectively influenced.

In a particularly preferred variant of the inventive method is provided that in a separate method ^¬ step, the thickness of a substantially flat portion of the LötStoppbarriere is modified so that the thickness of the solder ^¬ stop barrier of this substantially flat portion of the thickness substantially flat portion of the Menis ^¬ kusoberfläche, which defines the shape of the curved portion deviates. This can be done in particular by a differential printing, in which subsequently and in advance in the region of the substantially planar portion locally and defi ^¬ nated solder stop ink is applied to us cured.

The invention is explained below by means of figures representing exporting ^¬ approximately examples in more detail. It shows:

Fig. La: a schematic section of a first conductor ^¬ plate with solder pad and inventive solder stop barrier; Fig. Lb is a schematic diagram of a variant of the sanding ers ^¬ th circuit board having locally adapted breakdown ^¬ festigtkeit;

Fig. 2: a schematic micrograph of a second printed circuit board having printed conductor ^¬ and inventive electrical ^¬ shear insulating layer; a schematic section of a third conductor plate with solder pad and inventive solder stop barrier; a schematic cross-section of a fourth conductor plate with solder pad and inventive solder stop barrier; a schematic section of a fifth conductor plate with solder pad and inventive Lötstopp- barrier; and a schematic section of a sixth conductor plate with solder pad and inventive solder stop barrier;

Figure la shows a schematic sectional view of a printed ^¬ te 1 having a surface 2 on which an electrical contact in the form of solder pads 3 with contact surface 3a is arranged. The cross section of the solder pad 3 is substantially rectangular in this embodiment; the edges 3b, 3c of the solder pads which connect the contact surface 3a to the circuit board 1 duri ^¬ fen substantially perpendicular to the surface 2 of the printed ^¬ te. 1

Directly at the edge 3b, 3c of the solder pads 3 and continuously to the contact surface 3a then ei ^¬ ne designed as a solder resist barrier solder resist layer 4,5, the curved surfaces located respectively 4a, 5a each in the form of a con- kaven meniscus have whose Form is given by the Oberflächenwech ^¬ selwirkung the applied as a liquid solder stop ink with the solder pad 3 and the surrounding atmosphere. Accordingly, soldering produced in this way For example, capillary effects of the dissolving stop ink can also be used to achieve a desired connection to a soldering pad 3. Figure lb shows a variation of the first printed circuit board having locally adapted Durchschlagfestigtkeit, being used for identically ^¬ staltete components identical reference numerals. The difference from figure la is that here by ei ^¬ NEN differential pressure process according to the design of the solder ^¬ stop layers having curved surfaces 4a, 5a which in Figure la in accordance with the interface physics of this system in a planar We ^¬ sentlichen section with the Layer thickness zero überge ^¬ hen in a second printing process, a substantially planar portion 4b, 5b has been added, in which the Löstoppschicht the thickness t, ie one of the physically predetermined Me ^¬ niskusoberfläche in the plane extending section 4b, 5b differing thickness ^¬ has.

Figure 2 shows a schematic sectional view of a printed circuit board 6 having a surface 7, on which an electrical contact in the form of a conductor 8 is arranged, whose cross-section is substantially rectangular in this embodiment. The flanks 8b, 8c of the conductor track, which connect the surface 8a of the conductor track 8 of the printed circuit board 6 facing away from the printed circuit board 6, extend substantially perpendicular to the surface 7 of the printed circuit board 6.

Further, a LötStoppschicht is present, which forms an over the surface protruding portions of the conductor 8 electrically insulating insulation layer 9. The largest thickness D of the electrically insulating insulation layer 9 in the direction perpendicular to the surface 8 a of the conductor track 8 facing away from the printed circuit board 6 is about as thick as it is the thickness d of the electrically insulating insulating layer at the edges K1, K2 of the surface of the printed circuit board 6 from ^¬ facing surface 8a of the conductor 8 in the direction parallel to the surface 8a of the conductor and perpendicular to the edges K1, K2. Therefore, it is possible to achieve the desired Durchschlagfes ^¬ ACTION with a minimum cost of materials.

FIG. 3 shows a schematic sectional view of a printed circuit board 10 having a surface 11, on which two electrical contacts 12, which are designed as soldering pads, project in the direction perpendicular to the surface of the printed circuit board over the surface 11 of the printed circuit board 10 and a ^cone have contact surface 12a for electrical contact against this direction. The cross-section of the contacts 12 is substantially rectangular in this embodiment; the

Flanks 12b, 12c extending 12a connect the contact area with the printed ^¬ te 10 substantially perpendicular to the upper ^¬ surface 11 of the circuit board 10 between the electrical contacts 12 extends a

Solder-stop barrier 13, the surface 13a has the shape of a kon ^¬ kave meniscus, since it was generated by the application of a solder stop ink and subsequent curing. The shape is thus determined by the surface interaction of the liquid-applied solder stop ink with the electrical contacts 12 and the surrounding atmosphere. The ^¬ accordingly, for example, capillary effects of solder stop ^¬ ink can be used at a generated in this way solder resist barrier 13 to achieve a desired connection to the electrical contacts 12th

The embodiments shown in FIGS. 4 and 5 likewise each show schematic sectional views of printed circuit boards. th 20,30 on each of which two elekt ^¬ generic contacts 22,32 which are designed as solder pad with surfaces 21,31, angeord ^¬ net are in the direction perpendicular to the surface of the circuit board 21,31 20,30 over the surface 21, 31 of the circuit board 20,30 protrude and have a contact surface 22 a, 32 a for electrical ^¬ contacting contact against this direction.

Between the electrical contacts 22,32 extending each ^¬ weils a solder resist barrier 23,33, whose surface 23a, 33a in the form of a concave meniscus, as they bring by the on ^¬ a Lötstopptinte and then curing it was ^¬ testifies. The shape is thus determined by the Oberflä ^¬ chenwechselwirkung the applied as a liquid solder resist ink ^¬ with the electrical contacts 22,32 and the sur- rounding atmosphere.

If the shape of the solder resist barriers 23,33 in the figures 4 and 5 yet another and different from the shape of the ^¬ represent provided in Figure 1. The solder resist barrier 13, for example, which is the minimum thickness in the range between the electrical Kon ^¬ clock 22, 23 or the thickness in the edge region of the electrical contacts 22,23, this is in this Ausführungsbei ^¬ play on the different shape of the flanks

12b, 12c, 22b, 22c, 32b, 32c. In Figure 4, they are conically shaped, undercut in Figure 5.

Apart from such structuring of the flanks 12b, 12c, 22b, 22c, 32b, 32c of the electrical contacts 22, 23, there are also other possibilities for influencing the shape of the meniscus, for example by changes in viscosity or

Weight of the solder stop ink, choice of material for or ei ^¬ ne coating of the electrical contacts or influencing the atmospheric conditions during application of the solder stop ink. FIG. 6 shows a further exemplary embodiment. The schematic sectional view shown in this figure shows a circuit board 40 with surface 41 on the two electrical contacts 42, which are designed as Lötpads are arranged, which protrude in the direction perpendicular to the surface 41 of the circuit board 40 over the surface 41 of the circuit board 40 and a Have contact surface 42a for electrical contact against this direction.

In this embodiment, it is desirable that a flan ^¬ ke 42b, 42c of the electrical contacts 42 is wetted when establishing a connection via its contact surface with solder. The corresponding ^¬ is modeled between the electrical contacts 42 a solder resist barrier 43 made of solder resist ink, the surface 43a has the shape of a convex meniscus or droplet-shaped. Again, this is put on by the ^¬ a Lötstopptinte and then curing mög ^¬ Lich, which underscores the great freedom and adjustment possibilities for modeling of the solder stop barrier with the OF INVENTION ^¬ to the invention process clearly.

LIST OF REFERENCE NUMBERS

1, 6, 10,20,30,40 PCB

2,7,11,21,31,41 surface

3 solder pad

3a contact surface

3b, 3c flank

4.5 solder stop layer

4a, 5a curved surface

4b, 5b substantially planar section

8 trace

8a surface

8b, 8c flank

9 insulation layer

12, 22, 32, 42 electrical contact

12a, 22a, 32a, 42a contact surface

12b, 12c, 22b, 22c,

32b, 32c, 42b, 42c flank

13,23,33,43 solder-stop barrier

13a, 23a, 33a, 43a surface

Kl, K2 edge

D, d thickness

Claims

claims

Printed circuit board (1,6,10,20,30,40) with a surface (2,7,

11, 21, 31, 41) and with at least one electrical contact (12, 22, 32, 42) which is directed in the direction perpendicular to the surface (2, 7, 21, 21, 31, 41) of the printed circuit board (1, 6, 10,20,30,40) over the surface (2,7,11,21,31,41) of the printed circuit board (1,6,10,

20,30,40) protrudes,

wherein the electrical contact (12,22,32,42) is provided as a solder pad (3) with a contact surface (3a, 12a, 22a, 32a, 42a) for electrical contacting ^¬ rule against this direction from ^¬ designed or (as a conductor track 8 ) is configured, wherein the surface (2,7,11,21,31,41) of the printed circuit board (1,6,10,20,30,40) is at least partially covered with a solder stop ^¬ layer (4,5),

so that a solder resist barrier (13,23,33,43) for the min ^¬ least one electrical contact (12,22,32, 42) over the surface (2,7,11,21,31,41) the circuit board

(1,6,10,20,30,40) projects, is formed when this is designed as a solder pad (3) and / or so that one over the surface (2,7,11,21,31,41) the circuit board

(1,6,10,20,30,40) protruding portions of the conductor track electrically insulating insulation layer (9) is formed by the LötStoppschicht when the electrical con ^¬ tact is designed as a conductor track (8),

characterized in that the LötStoppschicht (4,5) consists of a hardened Lötstopptin ^¬ te and is designed so that the Lötstopp- barrier (13,23,33,43) at least partially a ge ^¬ curved surface (4a, 5a, 13a, 23a, 33a, 43a) which has the shape of a meniscus surface or droplet surface and / or that the solder resist layer (4,5) consists of an extended ^¬ cured Lötstopptinte and is designed that the greatest thickness (D) of the electrically insulating surface Iso ^¬ lationsschicht (9) in the direction perpendicular to that of the printed circuit board (6) facing away from (8a) of the conductors ^¬ web (8) is less than 125% of the thickness (d) of the electrically insulating insulation layer (9) at the edges (K1, K2) from the surface (7) of the circuitboard (6) abgewand ^¬ th surface (8a) (the conductor track (8) in the direction paral ^¬ lel to the surface (8a) of the conductor track 8) and perpendicular to the respective edge (K1, K2).

2. printed circuit board (1,6,10,20,30,40) according to claim 1,

characterized in that the ge ^¬ curved surface (4a, 5a, 13a, 23a, 33a, 43a) of the solder resist barrier (13,23,33,43) o- a convex meniscus surface of the drop surface.

3. printed circuit board (1,6,10,20,30,40) according to claim 1,

characterized in that the ge ^¬ curved surface (4a, 5a, 13a, 23a, 33a, 43a) of the solder resist barrier (13,23,33,43) is a concave meniscus surface.

4. printed circuit board (1,6,10,20,30,40) according to any one of the preceding claims,

characterized in that the soldering ^¬ stop barrier (13, 23, 33, 43) has a flank (12b, 12c, 22b, 22c, 32b, 32c, 42b, 42c) of at least (an electric Kon ^¬ clock 12,22,32 , 42).

5. printed circuit board (1,6,10,20,30,40) according to any one of the preceding claims, characterized in that the solder stop ^¬ barrier (13,23,33,43) steplessly and without overlapping to the contact surface (12a, 22a, 32a, 42a) connects.

6. printed circuit board (1,6,10,20,30,40) according to any one of the preceding claims,

That is, the edges (12b, 12c, 22b, 22c, 32b, 32c, 42b, 42c) of the at least one electrical contact (12, 22, 32, 42) are structured.

7. printed circuit board (1,6,10,20,30,40) according to any one of the preceding claims,

characterized in that the solder resist layer (4,5) is modeled in such a way that on un ^¬ terschiedlichen locations of the solder resist layer on the same printed circuit board (10,20,30,40) have different strengths breakdown ^¬ and / or supporting layer thicknesses are realized.

8. printed circuit board (1,6,10,20,30,40) according to any one of the preceding claims,

characterized in that the soldering ^¬ stop barrier (4b, 5b) has a substantially planar portion and the thickness of the solder stop barrier in the substantially planar portion of the thickness of a substantially flat portion of the meniscus upper ^¬ surface, the shape of the the curved surface (4a, 5a) pretends, deviates.

9. A method for at least partially coating egg ^¬ ner circuit board (1,6,10,20,30,40) according to any one of che Ansprü ^¬ che 1 to 8, characterized in that the soldering ^¬ stopper layer (4,5) is applied as a solder stop ink and cured from ^¬ .

10. The method according to claim 9,

characterized in that the soldering ^¬ stop ink is applied with an inkjet printer.

11. The method according to claim 10,

characterized in that the soldering ^¬ stop ink is applied in a 3D printing process.

12. The method according to any one of claims 9 to 11,

characterized in that prior to the application of the solder stop ink, the flanks (12b, 12c, 22b, 22c, 32b, 32c, 42b, 42c) of the at least one electrical Kon ^¬ clockt (12,22,32,42) are at least partially structured.

13. The method according to any one of claims 9 to 12,

characterized in that in a separate process step, the thickness (t) of a wesent ^¬ union planar portion (4b, 5b) of the LötStoppbarriere mo ^{¬ is} modified so that the thickness (t) of the solder stop barrier in this substantially planar portion

(4b, 5b) of the thickness of a substantially planar Ab ^{¬ section of} the meniscus surface, which dictates the shape of the curved ^¬ th surface (4a, 5a) deviates.