Method for obtaining information about organic solderability preservatives on printed circuit boards

Abstract

The present invention relates to a method for obtaining information about an organic solderability protection (OSP) layer on a printed circuit board (PCB), the method comprising: providing a PCB (16) having a copper layer (18), wherein a solder resist (19) is placed on the copper layer (18), and the solder resist (19) has an opening (21), wherein the copper surface of the copper layer (18) in the opening (21) is covered by the OSP layer; providing a fluorescence measurement system (10), which comprises a radiation source (11), a detection unit (12) and a moving device (24), the method comprising: a) obtaining (S2) information about the position of the openings (21) on the PCB (16), b) selecting (S3) at least one of the openings (21), c) placing (S4) the radiation source (11) at a position where a radiation beam (22) irradiates into at least one selected opening (21) on the OSP layer (20), and d) detecting (S5) fluorescent radiation (23) emitted from the OSP (20).

Description

Technical Field

[0001] The present invention relates to a method for obtaining information about an organic solderability preservative on a printed circuit board, and more particularly to a method for determining the individual thickness of an organic solderability preservative (OSP) on a printed circuit board. Background Art

[0002] A printed circuit board (PCB) includes copper structures, such as copper conductive paths, which are placed on a non-conductive substrate. A solder resist is placed on the printed circuit board and covers the substrate and most of the copper structures. The solder resist includes openings for copper that are not covered by the solder resist. These openings allow access to contact pads. Contact pads are junctions for establishing contact from the copper structures of the PCB to electronic components placed on the PCB and connected to the PCB by solder connections. The contact pads may have a smaller or larger area than the allocated openings. To establish solder connections, the openings are filled with solder paste, the components are inserted and connected by reflow soldering.

[0003] Before electronic components are connected to the PCB, the PCB may be stored for weeks or months. During that time, the exposed copper in the contact pads that are not covered by the solder resist will oxidize, which will make a reliable solder connection impossible. This is why the contact pads are temporarily protected by so-called organic solderability preservatives (OSP). The PCB is immersed in an OSP solution and the OSP is deposited exclusively on the exposed copper in the contact pads by reacting with the copper. Thus, the OSP exclusively fills the openings and covers the copper surfaces of the contact pads in the openings. In the subsequent soldering process, the OSP evaporates, decomposes or mixes with other components without affecting the solder resist on the PCB.

[0004] It is necessary to know whether the copper of the contact pads is adequately covered by OSP to ensure the subsequent functionality of the PCB. It is particularly desirable to know the thickness of the OSP layer on the contact pads. Although it is desirable to have the same OSP thickness on all contact pads, openings with varying sizes typically result in OSP with varying thicknesses. For these reasons, a fast and reliable method for determining the individual thickness of the OSP is highly desirable.

[0005] In a process according to the current state-of-the-art technology, the thickness of the OSP is determined by cutting or grinding the contact pads and measuring the OSP thickness by electron microscopy. The disadvantage of said method is that the measurement process destroys the PCB and the analysis is expensive, time-consuming and complicated. In another technique, the OSP is chemically dissolved and the concentration of the dissolved compounds forming the OSP is determined. From the concentration of said compounds, the average thickness of the OSP in the contact pad is calculated. The obvious disadvantage of said method is that, in addition to at least destroying the OSP, only the average thickness and the theoretical thickness are determined. Although it is a fast method, it is not possible to determine the individual thickness of a specific OSP in a specific opening. In addition, these techniques are only suitable for random sampling. In addition, it is not possible to implement such a method for active real-time inspection.

[0006] In other methods, non-destructive methods are used. For example, US 2006 / 023936 A1 relates to a film inspection device, an inspection system, and a method of inspecting a printed circuit board for inspecting an organic film formed on a printed circuit board.

[0007] US 2012 / 092488 A1 relates to a precision solder resist alignment inspection method, including a method for operating a machine vision inspection system to determine a fluorescent imaging height to acquire a fluorescent image to repeatedly determine the position of a workpiece feature edge located in a fluorescent material layer on the workpiece.

[0008] Invention goal

[0009] The object of the present invention is to provide an improved and significantly simplified method for obtaining information about an organic solderability preservative on a printed circuit board, in particular for determining the individual thickness of an organic solderability preservative on a printed circuit board, thereby avoiding the above-mentioned disadvantages. It is particularly desirable to utilize such a simplified method as an active manufacturing control. In particular, another object is to provide an improved method for obtaining a thickness profile of an OSP layer. Summary of the invention

[0010] The present invention provides a method for obtaining information about an organic solderability resist on a printed circuit board according to technical solution 1. Specific embodiments are the objects of the attached technical solutions or are described in this patent specification.

[0011] Therefore, the present invention provides a method for obtaining information about an organic solderability preservative on a printed circuit board, the method comprising:

[0012] - providing or producing a printed circuit board having a copper layer covering a part of the area of ​​the printed circuit board,

[0013] wherein the solder resist is placed on the copper layer, and the solder resist has an opening, wherein the copper surface of the copper layer in the opening is covered with an organic solderability protective layer having a separate thickness,

[0014] -Provide fluorescence measurement system, including

[0015] a radiation source adapted to emit a radiation beam,

[0016] a detection unit for detecting fluorescent radiation, and

[0017] The moving device is configured to move the radiation source and the printed circuit board relative to each other in at least one dimension, and the method comprises the following steps

[0018] a) obtaining information about the location of the openings on the printed circuit board,

[0019] b) selecting at least one of the openings, thereby obtaining at least one selected opening,

[0020] c) using a moving device to move the radiation source and the printed circuit board relative to each other and placing the radiation source at the position where the radiation beam impinges into the at least one selected opening and on the organic solderability resist in the at least one selected opening,

[0021] d) detecting fluorescent radiation emitted from the organic solder preservative with a detection unit.

[0022] The detected fluorescent radiation is preferably used as information in quality control and in further production and processing of the OSP layer on the PCB. A further explanation is given below. When detecting fluorescent radiation, preferably the signal is detected, in particular the intensity of the signal.

[0023] In a specific embodiment, the method is a method for determining an individual thickness of an organic solderability preservative layer, the method further comprising the steps of:

[0024] e) determining an individual thickness of the organic solderability preservative layer within at least one selected opening.

[0025] By means of the method, the individual thickness of the OSP layer is determined, preferably within each selected opening, with the aid of fluorescent radiation.

[0026] The term "individual thickness" means the thickness in a selected opening. The term individual indicates that different thicknesses of the OSP layer may occur in different openings, so the thickness is an individual thickness.

[0027] The method of the present invention is carried out without damaging or destroying the printed circuit board.

[0028] In said method, the measuring system, in particular the radiation source, is preferably moved at any surface location of the PCB and the individual thickness of the OSP is preferably determined at any desired location with an opening in the solder resist.

[0029] The method allows the determination of the individual thickness of the OSP layer on the PCB with preferably high resolution, thereby avoiding erroneous readings due to complete or partial illumination of the solder resist. Solder resist compounds usually emit fluorescent radiation upon excitation. Therefore, if the solder resist is (also) illuminated instead of or together with the OSP, erroneous results will be obtained. This can be avoided by the method of the invention.

[0030] The method of the invention is a non-destructive method for determining layer thickness and preferably also for determining the thickness distribution of an OSP on a PCB. The method significantly increases process reliability and helps save chemicals and resources.

[0031] Through the greater reliability of the method, the thickness of the OSP can be adjusted more accurately, rather than having to build a thicker OSP as needed to guarantee a minimum thickness.

[0032] The method of the invention is rapid, inexpensive and significantly simpler, preferably compared to methods used in the art, which method furthermore allows large-scale production control. DETAILED DESCRIPTION

[0033] In the fluorescence measurement system, the radiation source emitting the radiation beam preferably emits radiation in the UV range. The radiation source is preferably a laser. Preferably, the radiation source most preferably has a power of up to 150 mW. Preferred is the method of the invention, wherein the radiation beam has a power in the range of 20 mW to 200 mW, preferably in the range of 40 mW to 180 mW, more preferably in the range of 60 mW to 160 mW, most preferably in the range of 80 mW to 140 mW.

[0034] The radiation beam preferably irradiates the organic solderability resist layer 0.5 to 1 mm above the surface. 2 area.

[0035] The opening preferably has a width of at least 1 mm 2 area, most preferably at least one selected opening has an area of ​​at least 1 mm 2 The upper limit of the area is preferably 100 mm 2 .

[0036] The radiation beam causes fluorescent radiation within the selected / irradiated openings and the fluorescent radiation is emitted from the OSP and detected by the detection unit.

[0037] The detection unit is preferably a photodiode.

[0038] By means of the moving device, the radiation source and the PCB are moved relative to each other, so that in this relative movement the radiation source moves along the surface of the PCB or adjacent to the surface of the PCB without contacting the PCB.

[0039] One of the radiation source and the PCB is preferably kept in a fixed position and the other is moved by a moving device. In another embodiment, both the radiation source and the PCB are moved by a moving device.

[0040] Preferably, the radiation source is coupled to the mobile device.

[0041] The method preferably further comprises: placing the printed circuit board adjacent to the moving device.The described embodiment is preferably applied when the printed circuit board is stationary in a stationary position and the fluorescence measurement system is moved by the moving device.

[0042] Preferably, the moving means are configured to move relative to each other in at least two dimensions.

[0043] - radiation source and detection unit, and

[0044] -Printed circuit boards.

[0045] The two-dimensional movement is preferably in such a way that the distance between the radiation source and the PCB, in particular the surface of the PCB, remains constant or substantially constant during the movement.

[0046] In the chosen Cartesian coordinate system, the PCB (particularly the copper layer and OSP layer) preferably extends in the X and Y directions (wherein the PCB and layers of course have thickness in the Z direction) and relative movement is preferably accomplished in one or more of the X and Y directions.

[0047] Preferably, the movement is also in a third dimension. In a Cartesian coordinate system, the PCB preferably extends in the X and Y directions and the relative movement is preferably performed in one or more of the X, Y and Z directions. Movement in the Z direction allows adapting the method to different thicknesses of the PCB at the location of determining the thickness of the OSP or during the relative movement.

[0048] The moving device preferably comprises holding means for holding the radiation source and preferably also comprises a detection unit.

[0049] The movement means preferably comprises a linear guide allowing movement of one or more of

[0050] - a radiation source and preferably also a detection unit,

[0051] -PCB.

[0052] The moving device preferably comprises a motor and / or a gear mechanism for achieving the movement.

[0053] The movement means preferably allows movement in steps of 0.1 to 0.5 mm in one direction.

[0054] In each case, the opening has a position on the PCB, preferably relative to at least two side edges of the PCB, wherein each opening has individual information about its position. There are different possibilities for obtaining information about the position of the openings on the printed circuit board. One possibility is a visual inspection. For the visual inspection, a camera is preferably used.

[0055] Another possibility is that the information about the position of the opening is included in the data set. Therefore, in step a), information about the position of the opening is preferably obtained from the data set. Based on said information, the selection in step b) is performed.

[0056] The data set preferably comprises information about the positions in the Gerber format. This is an open ASCII vector format for 2D binary images.

[0057] The selection of at least one (i.e. one or more than one) opening in step b) is preferably done by individual decision or by a programmed procedure or workflow. For example, when information about the position of the opening is available from the mentioned data set, such information is preferably used as the basis for the selection in step b). Preferably, the selection step b) therefore comprises selecting several openings in a predetermined order. The order is preferably an order of size or an order of position on the PCB.

[0058] Once at least one of the openings is selected, the next step is preferably to move the radiation source and the printed circuit board relative to each other using a moving device and to place the radiation source at the position where the radiation beam impinges into the at least one selected opening and onto the organic solderability resist within the at least one selected opening.

[0059] The method of the invention allows to specifically irradiate the organic solderability preservative layer. Irradiating the solder resist or another solder resist would lead to an erroneous thickness determination. Therefore, the radiation source is preferably placed in such a way that the solder resist is not irradiated.

[0060] Preferably the method of the invention, wherein in step c) the radiation beam is irradiated in such a way that the solder resist is not irradiated. With the method of the invention, since the measuring system allows high resolution, for example when the radiation beam irradiates only 0.5 to 1 mm 2 When measuring the area of ​​a vehicle, the thickness can also be determined in extremely small openings.

[0061] When the fluorescent radiation emitted from the organic solder preservative is detected with the detection unit in step d), preferably the signal, in particular the intensity of the fluorescent radiation, is detected.

[0062] When determining the thickness of the OSP layer, preferably the intensity detected in step d) is preferably assigned to the thickness of the OSP layer. In other words, the thickness of the layer is preferably determined from the intensity of the fluorescent radiation. In yet other words, preferably the intensity detected in step d) is preferably arranged in relation to the thickness of the OSP layer to determine the thickness of the OSP layer. Preferably, the intensity depends on the thickness of the layer. The dependence of the intensity on the thickness is preferably obtained by calibration, which will be further described below.

[0063] Preferably, after each step d), the detected fluorescent radiation, preferably the intensity, forms read data, which is more preferably further processed into processed read data. More preferably, in a subsequent step, the read data and the processed read data are arranged in relation to reference read data and processed reference read data, respectively. Most preferably, in the method of the invention, the read data and the processed read data, respectively, are arranged in relation to reference read data and processed reference read data, respectively, obtained from a reference sample having at least one reference organic solderability preservative layer with a known reference thickness. Thereby, the individual thickness of the organic solderability preservative layer is determined.

[0064] In order to deduce the thickness of the OSP layer from the fluorescent radiation (in particular the radiation intensity), a calibration is preferably performed. The method preferably comprises

[0065] - detecting reference fluorescence radiation of different reference samples of a reference organic solderability preservative layer, wherein in each of said reference samples said reference layer has a known thickness. For said step, preferably a fluorescence measurement system is used, said fluorescence measurement system also being used to determine the individual thicknesses of the organic solderability preservative layers

[0066] - Obtain an assignment of the reference fluorescent radiation to the thickness of the organic solderability preservative layer.

[0067] The assigned values ​​are preferably used as reference, in other words as reference information.

[0068] A "known thickness" is preferably a thickness determined by another method. For example, the OSP layer of a reference sample is preferably examined by microscopy, such as cutting or grinding the layer and measuring the individual layer thicknesses by microscopy.

[0069] The assignment is preferably expressed as an assignment of values, for example in a calibration data table as a calibration curve, or as a mathematical relationship. In a simple embodiment, the assignment is a linear relationship.

[0070] In the method of the invention, a PCB is provided or produced. In the latter case, the manufacture of the printed circuit board preferably comprises depositing an organic solderability preservative layer within the opening and on the copper surface of the copper layer within the opening.

[0071] The individual thicknesses are preferably determined on the basis of the assigned information.

[0072] This is preferably accomplished by

[0073] - Comparing the detected values ​​of the fluorescent radiation of step d) with the assigned values ​​in order to find identical values ​​in the assigned values. In case exactly the same values ​​are not detected when establishing the assigned values, the values ​​in the assigned values ​​may be interpolated values.

[0074] -Identify the assigned thickness in the assignment.

[0075] In one embodiment of the invention, the method comprises checking

[0076] - the signal or intensity of the fluorescent radiation detected in step d), and / or

[0077] - the individual thickness of the organic solderability preservative layer determined in step e)

[0078] Is it within the required range or rated range.

[0079] The information is preferably used for quality control, as information for trimming the PCB used in the method and / or as information for influencing the production process of further PCBs.

[0080] The signal or intensity obtained when detecting the fluorescent radiation in step d) can be used as information about the thickness or quality of the OSP layer without actually determining the thickness. For example, an intensity outside the desired or nominal range can indicate that the thickness of the OSP layer is too low or too high.

[0081] Preferably, the method further comprises one or more of the following steps:

[0082] i) Discarding printed circuit boards

[0083] ii) trimming printed circuit boards to change the individual thickness of the organic solderability preservative layer,

[0084] iii) adapting the method of producing the organic solderability preservative on at least one further printed circuit board so as to obtain an individual thickness of the organic solderability preservative on the at least one further printed circuit board within a desired range or a nominal range.

[0085] Changing thickness results in a changing signal or changing fluorescence radiation intensity. When inspecting or re-inspecting a PCB with a changed OSP thickness, this results in a changed signal or fluorescence radiation intensity and it can be determined whether the signal or intensity is within the desired or rated range without (re)determining the thickness.

[0086] In case i), if the layers are made thinner or thicker as required, the PCB is discarded.

[0087] In case ii), the method is also referred to as a method for producing an organic solderability resist on a printed circuit board, the method comprising determining the individual thickness of the organic solderability resist on the printed circuit board. The PCB is returned to the step of producing the organic solderability resist.

[0088] In case ii), the thickness of the OSP layer is preferably increased.

[0089] In case iii), the method is also referred to as a method for producing an organic solderability preservative on a printed circuit board, the method comprising determining the individual thickness of the organic solderability preservative on the printed circuit board.

[0090] In case iii), the production method is adapted to achieve the desired thickness, as described further below. This is preferably done by adapting the deposition within the openings so that the OSP layer in the further PCB has an increased thickness or a reduced thickness compared to the thickness before the adaptation.

[0091] For example, the production of OSP is done by deposition. Deposition is preferably done by immersion in a solution of an OSP forming compound. If the thickness is outside the desired or rated range, the parameters of the method for depositing the organic solderability preservative are preferably changed.

[0092] Changing the production process in iii) preferably comprises one or more of the following measures:

[0093] - interruption of OSP production process,

[0094] - varying the concentration of an OSP-forming compound in a solution comprising the OSP-forming compound

[0095] - Varying the process time, in particular the immersion time in the solution containing the OSP forming compound

[0096] -Change process temperature

[0097] - Changing the pH of a solution containing an OSP-forming compound

[0098] In one embodiment, the method of the present invention comprises

[0099] - providing information about the position of at least one selected opening in the printed circuit board to a controller, said controller controlling the movement of the radiation source and the printed circuit board relative to each other,

[0100] Wherein, in step c), the movement of the radiation source and the printed circuit board relative to each other and the placement of the radiation source are controlled by a controller. The controller is preferably part of the mobile device or part of another device, such as a computer connected to the mobile device.

[0101] Preferably, the method comprises determining the individual thicknesses of the OSP at different locations within at least one selected opening. This allows a thickness profile of the OSP within the opening to be obtained.

[0102] The information for the controller is preferably provided from the data set mentioned above. The information is preferably provided in a predetermined or programmed manner or in a predetermined or programmed sequence. This allows automation of the process, in particular when determining the thickness of the OSP in more than one opening or when determining the thickness in one opening at different positions, and / or when determining the thickness of multiple PCBs. The sequence of openings on the PCB and / or the desired position of the radiation on the PCB are preferably defined and used as information for controlling the process, in particular the relative movement of the radiation source and the PCB and the radiation of the radiation beam by the radiation source.

[0103] In one embodiment of the method of the invention, steps b) to d) are repeated one or more times, wherein in each repetition of step b) it is repeated once again, which means that different openings are selected and the thickness of the organic solderability preservative is determined at each irradiation position within the further openings. In said embodiment, the thickness within a plurality of openings is preferably determined in a predetermined sequence. Preferably a data set and a controller as mentioned above are used. When steps b) to d) are repeated in a repetition of step b), the thickness of the organic solderability preservative is preferably determined based on a sequence of different openings and preferably at each irradiation position within the different openings.

[0104] In a more specific embodiment, the further opening (or in case of more repetitions, the plurality of further openings) have different areas, and the method further comprises:

[0105] - Determine the assignment between the area of ​​the opening and the thickness of the organic solderability preservative layer.

[0106] Ideally, the thickness of the OSP layer should not, or at least not strongly, depend on the area of ​​the opening or on the area of ​​the OSP layer. Knowledge about such assignments provides information on how the manufacturing process of the OSP can be influenced to achieve this.

[0107] In another embodiment of the method of the invention, steps b) to d) are repeated one or more times, wherein in each repetition of step b) the same opening is selected and in step c) the radiation source is moved to a different position, thereby irradiating different positions on the organic solderability preservative within the same opening. In said embodiment, preferably the thickness of the OSP at a plurality of positions within the opening is determined preferably in a predetermined order. Preferably a data set and a controller as mentioned above are used. Of course said embodiment can be combined with an embodiment for determining the thickness of the OSP. Of course said embodiment can be combined with the previous embodiment for determining the thickness within different openings.

[0108] The solder resist is not limited in any way. The solder resist preferably contains epoxy resin.

[0109] The organic solderability preservative of a defined thickness within the opening is a solid substance, in particular a solid layer.Preferred is the method of the invention, wherein the organic solderability preservative within the opening is a polymerized and cured layer.

[0110] In one embodiment of the method, the organic solderability preservative (OSP) comprises an imidazole compound and / or a benzimidazole compound. The imidazole compound and / or the benzimidazole compound is preferably the main component of the OSP, which means that it constitutes at least 50% by weight of the OSP. Another component of the OSP is Cu(I), which originates from the copper forming the surface of the OSP.

[0111] Cu(I) preferably forms a complex with an imidazole and / or benzimidazole compound. The organic solderability preservative preferably comprises an imidazole-Cu(I) complex and / or a benzimidazole-Cu(I) complex. The organic solderability preservative layer is preferably at least partially an organometallic layer. The organometallic layer comprises copper as metal. The organometallic layer preferably exhibits a gradient of copper(I) concentration, the concentration preferably decreasing in a direction relative to the outer surface of the layer.

[0112] Therefore, the OSP layer is preferably formed not only from compounds (such as (benzi)imidazole) deposited on copper when forming the OSP layer, but also from copper from the copper layer itself, thereby forming a complex layer. Using the method of the present invention, the individual thickness of the complex layer can be determined with high accuracy.

[0113] The imidazole compound is preferably an alkyl imidazole, in particular selected from the group consisting of ethyl imidazole, propyl imidazole, butyl imidazole, and pentyl imidazole. The benzimidazole compound is preferably an alkyl benzimidazole, in particular selected from the group consisting of ethyl benzimidazole, propyl benzimidazole, butyl benzimidazole, and pentyl benzimidazole.

[0114] The benzimidazole compound is preferably a halogen benzimidazole, in particular a chlorobenzimidazole. The benzimidazole compound is preferably a substituted or unsubstituted arylbenzimidazole, in particular selected from the group consisting of phenylbenzimidazole, diphenylbenzimidazole, chlorobenzylbenzimidazole, chlorophenylbenzimidazole, dichlorobenzyl-benzimidazole.

[0115] The organic solderability preservative preferably does not contain epoxy resin.

[0116] The organic solderability preservative preferably comprises an iodide.

[0117] The thickness of the OSP layer to be determined is preferably in the range of 50 to 500 nm, more preferably in the range of 100 nm to 470 nm, even more preferably in the range of 150 nm to 450 nm, still more preferably in the range of 200 nm to 430 nm, most preferably in the range of 250 nm to 410 nm.

[0118] In the method of the present invention, preferably in all openings, the copper surface of the copper layer is covered with an organic solderability protective layer. This is most preferred because instead of conventionally covering these openings with tin, tin alloy, nickel, gold or a combination thereof, the organic solderability protective agent is preferably used to temporarily prevent oxidation of the copper surface. Therefore, it is preferred that the method of the present invention, wherein the printed circuit board does not include an opening covered with tin, tin alloy, nickel, gold or a combination thereof before forming the OSP layer in the opening.

[0119] Preferred is the method of the present invention, wherein said radiation beam has a wavelength in the range of 250 nm to 450 nm, preferably in the range of 300 nm to 400 nm, most preferably in the range of 350 nm to 375 nm.

[0120] Preferred is the method of the present invention, wherein said fluorescent radiation has a wavelength in the range of 350 nm to 550 nm, preferably in the range of 400 nm to 520 nm, most preferably in the range of 450 nm to 470 nm.

[0121] Preferably, the wavelength of the radiation beam is different from the wavelength of the fluorescent radiation. More preferably the method of the present invention, wherein the wavelength of the radiation beam is less than the wavelength of the fluorescent radiation. Most preferably the method of the present invention, wherein the wavelength of the radiation beam is in the range of 350nm to 375nm and the wavelength of the fluorescent radiation is in the range of 450nm to 470nm.

[0122] As mentioned above, the method of the invention is a non-destructive method. Therefore, preferred is the method of the invention, wherein in step c), the organic solderability preservative layer is not removed, that is, neither partially nor completely.

[0123] Preferred is the method of the present invention, wherein said radiation beam is not an X-ray radiation beam.

[0124] Preferred is the method of the invention, wherein more than one individual thickness is determined and these are provided as individual thickness distributions.

[0125] Preferred is the method of the invention, wherein the fluorescent radiation detected in step d) is linearly related to the individual thickness of the organic solderability preservative layer. Figure 3 confirmed in .

[0126] Preferred is the method of the invention, wherein at least a plurality of openings are filled with a pre-solder and preferably subjected to a heat treatment to obtain pre-solder openings, wherein during the heat treatment the organic solderability preservative is decomposed.Preferably, the pre-solder comprises tin and / or nickel. BRIEF DESCRIPTION OF THE DRAWINGS

[0127] Figure 1 Schematically showing the configuration of a printed circuit board and a fluorescence measurement system used in the method of the present invention;

[0128] Figure 2 A fluorescence measurement system, a printed circuit board, and a mobile device are shown in a specific embodiment of the method of the present invention;

[0129] Figure 3 Displays the calibration line of the SITA cleano spector relative to the layer thickness of the OSP;

[0130] Figure 4 Displays a top view of the PCB and multiple measurement points on it;

[0131] Figure 5 An overview of the steps of the method of the present invention is shown.

[0132] Examples

[0133] The fluorescence measurement system is a cleanliness meter from SITA Company. It is a laser-based fluorescence measuring head.

[0134] Measuring principle:

[0135] The principle is shown in Figure 1 The analyte cleanliness instrument uses an excitation frequency of 365 nm and detects the light emitted from each substrate at a frequency of 460 nm. Beam guidance and various filters ensure that only the emitted light reaches the detector. It can record values ​​between 0 and 2000 RFU (Relative Fluorescence Units).

[0136] As the layer thickness of the OSP increases, the increasing RFU is recorded or output. The layer thickness of the OSP can be determined with the aid of standards and calibration lines.

[0137] exist Figure 1 The following components are displayed:

[0138] 10 Fluorescence measurement system

[0139] 11. Radiation source, emitting radiation beam

[0140] 12 Detection unit, which is preferably an optical detection unit

[0141] 13 Low-pass filter

[0142] 14 High-pass filter

[0143] 15 Half mirror

[0144] 16 Printed Circuit Board (PCB)

[0145] 17 Substrate for copper layer (part of PCB)

[0146] 18 Copper layer, part of PCB

[0147] 19 Solder resist, PCB part

[0148] 20 Organic solderability preservative (OSP)

[0149] 21 Opening (in this cross-sectional view, the edge of the opening) allowing access to the contact pad

[0150] 22 Radiation beam, UV light

[0151] 23 Fluorescence radiation

[0152] Figure 2 The measuring system 10 and a moving device 24 are shown. The moving device 24 includes a holding device 25 to which the measuring system 10 is connected by a fixing member. The holding device can be moved along a guide 26 in a direction Y and along another guide (not shown) in a direction X perpendicular to Y (a coordinate system is shown). The movement is achieved by a motor and a gear mechanism (not shown). The printed circuit board 16 is oriented in the XY direction so that the fluorescence measuring system 10 can be moved by the moving device 24 to any position across and above the printed circuit board 16.

[0153] Example 1 (Calibration)

[0154] Four FR4 base material samples (5x5 cm) each with 35 μm copper foil were treated with organic solderability preservative Atotech OS Tech with different OSP layer thicknesses. The thickness of the OSP layer is derived from the different deposition times ranging from 15 seconds to 120 seconds. The main component of the OSP is 2-[(4-chlorophenyl)methyl]-1H-benzimidazole. Table 1 shows the results.

[0155] Method 1 (not according to the invention): The entire OSP is stripped with 0.5% HCl and based on the UV determined concentration measured at 270 nm in a defined volume. Thus, the average layer thickness is calculated. This is used to establish a calibration curve ( Figure 3 )

[0156] Method 2 (not according to the invention): Production of cross sections and determination of layer thicknesses by means of a scanning electron microscope (FIB).

[0157] Method 3 (according to the present invention): SITA Cleano Spector ( Figure 1 ); Correlate the results of method 1 with those of method 3.

[0158] Table 1: Results

[0159]

[0160]

[0161] Figure 3 is the calibration line that sets the measured RFU to be related to the thickness measurement according to Method 1. * indicates other results obtained by Method 2.

[0162] Example 1 shows a very reliable correlation.

[0163] Example 2

[0164] The layer thickness distribution was determined on the printed circuit board with the aid of two methods. For this purpose, measurements were performed on different and similar openings in the printed circuit board that were covered with OSP.

[0165] Figure 4 A top view of the PCB is shown with measurement points 1 to 9. Each measurement point is located in a different opening where no solder resist 19 has been deposited, the openings being labeled 1' to 9'. Some of the openings in the area 1' to 9' are different. Parts of the copper are covered by the solder resist 19, such as the covered conductive path 27.

[0166] Table 2: Structure

[0167]

[0168] The thickness according to method 3 is the same as that used in Example 1 ( Figure 3 ) is obtained by calibration.

[0169] It can be seen that the thickness of the OSP layer in the openings and on the contact pads depends on the size of the openings. For example, the thickness in the larger openings 8' and 9' (measurement points 8 and 9) is smaller than the thickness in the smaller openings 1' to 3' (measurement points 1 to 3). Therefore, a great advantage of the method of the invention is the reliable determination of the individual thicknesses.

[0170] It can be seen that in the opening with the largest area (measurement point 9) the layer thickness increases compared to the smaller opening with measurement point 8. This is an unexpected result but shows the advantage of the method of the invention which allows the determination of individual thicknesses in individual openings and allows the determination of these unexpected results which can be used as a basis for adapting the production process for OSP layers on PCBs.

[0171] Figure 5 An overview of the overall method of the present invention in a basic embodiment is shown. With reference to the previous drawings, in particular Figure 1 and 2 , and previous examples.

[0172] S1: Place the printed circuit board 16 adjacent to the moving device 24 of the fluorescence measurement system 10. Figure 2 middle

[0173] S2: Get information about the opening position on the printed circuit board 16, where preferably data from a data set (Gerber data set) is provided to a controller (not shown), which for example controls the movement of the moving device 24. The data is preferably selected by a program. As an alternative, the information can be obtained by visually inspecting the PCB 16 with a camera.

[0174] S3: Selecting at least one of the openings 21. The selection is preferably done by a personal decision or by a computer program.

[0175] S4: Preferably, the radiation source 11 is moved by the moving device 24, and the radiation source is placed in a position such that the radiation beam 22 is irradiated into at least one selected opening 21 and is located on the organic solderability protective layer 20 in at least one selected opening, such as Figure 1 and 2 as shown in the .

[0176] S5: Figure 1 As shown in FIG. 1 , fluorescent radiation 23 emitted from organic solder preservative 20 is detected by detection unit 12 .

[0177] S6: Determine the individual thickness of the organic solderability preservative layer 20 at the irradiated position within at least one selected opening 21. This point is explained in Examples 1 and 2 above.

[0178] Preferably, steps S3 to S6 are repeated, for example in different openings and / or at different measuring points, for example 1 to 9, such as Figure 4 as shown in the .

Claims

1. A method for obtaining information about a layer of organic solderability preservative on a printed circuit board, the method comprising - providing or producing a printed circuit board (16) having a copper layer (18) covering a part of the area of ​​the printed circuit board (16), wherein a solder resist (19) is placed on the copper layer (18), and the solder resist (19) has an opening (21), wherein the copper surface of the copper layer (18) in the opening (21) is covered by a layer of an organic solderability preservative (20) having a respective thickness, - providing a fluorescence measurement system (10), comprising a radiation source (11) adapted to emit a radiation beam (22), a detection unit (12) for detecting fluorescent radiation (23), and a moving device (24) configured to move the radiation source (11) and the printed circuit board (16) relative to each other in at least one dimension, The method comprises the following steps a) obtaining (S2) information about the position of the opening (21) on the printed circuit board (16), b) selecting (S3) at least one of the openings (21) so as to obtain at least one selected opening, c) using the moving device (24) to move the radiation source (11) and the printed circuit board (16) relative to each other (S4) and placing the radiation source (11) at a position where the radiation beam (22) irradiates into the at least one selected opening (21) and on the layer of the organic solderability preservative (20) in the at least one selected opening, d) detecting (S5) the fluorescent radiation (23) emitted from the organic solderability preservative (20) with the detection unit (12), Wherein in step c), the radiation beam (22) is irradiated in a manner such that the solder resist (19) is not irradiated.

2. The method according to claim 1, wherein the method is a method for determining the individual thickness of the layer of the organic solderability preservative, the method further comprising the steps of: e) determining (S6) the individual thickness of the layer of organic solder preservative (20) in the at least one selected opening.

3. The method according to claim 1 or 2, comprising: - detecting a reference fluorescence radiation of different reference samples of a reference layer of an organic solder preservative, wherein in each of said reference samples said reference layer has a known thickness, - obtaining an assignment of the thickness of the reference fluorescent radiation to the layer of organic solderability preservative. The method according to claim 3 , wherein the individual thickness is determined based on the assigned value.

5. The method according to claim 1 or 2, comprising checking - the signal or intensity of said fluorescent radiation detected in step d), and / or - the individual thicknesses of the layers of organic solderability preservative determined in step e) Is it within the required range or rated range.

6. The method of claim 5, further comprising one or more of the following steps: i) discarding the printed circuit board (16) ii) trimming the printed circuit board (16) to change the individual thicknesses of the layers of organic solder preservative, iii) adapting the method for producing a layer of organic solder preservative on at least one further printed circuit board so as to obtain a layer of organic solder preservative of a respective thickness within said desired or nominal range on said at least one further printed circuit board.

7. The method according to claim 1 or 2, wherein the information about the position of the opening is included in a data set, and in step a), the information about the position of the opening is obtained from the data set.

8. The method according to claim 1 or 2, comprising: - providing information about the location of said at least one selected opening on said printed circuit board to a controller, The controller controls the movement of the radiation source (11) and the printed circuit board (16) relative to each other, in, In step c), the movement of the radiation source (11) and the printed circuit board (16) relative to each other and the placement of the radiation source are controlled by the controller.

9. The method of claim 2, wherein steps b) to d) are repeated one or more times, wherein in each repetition of step b) a further opening is selected and wherein each irradiation position in the further opening determines the thickness of the layer of organic solderability preservative.

10. The method of claim 9, wherein the additional opening, or in the case of more repetitions, the additional opening has a different area, the method further comprising: - Determining an assignment between the area of ​​the opening and the thickness of the layer of organic solderability preservative.

11. The method according to claim 1 or 2, wherein steps b) to d) are repeated one or more times, wherein the same opening is selected in each repetition of step b) and the radiation source is moved to a different position in step c), thereby irradiating different positions on the layer of organic solderability preservative within the same opening. 12 . The method according to claim 1 , wherein the organic solderability preservative comprises an imidazole compound and / or a benzimidazole compound.

13. The method according to claim 1 or 2, wherein the organic solderability preservative comprises an imidazole-Cu(I) complex and / or a benzimidazole-Cu(I) complex, wherein the layer of the organic solderability preservative is at least partially an organic metal layer.

14. The method according to claim 1 or 2, wherein the radiation beam irradiates 0.5 to 1 mm above the layer of organic solderability preservative. 2 area.

15. The method according to claim 1 or 2, wherein manufacturing the printed circuit board (16) includes depositing (S0) a layer of organic solderability preservative (20) in the opening (21) and on the copper surface of the copper layer (18) within the opening (21).

16. The method according to claim 1 or 2, wherein the at least one selected opening (21) has a diameter of at least 1 mm. 2 area.

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