JPS5919479B2 - How to print thick film circuits - Google Patents

Description

[Detailed description of the invention] The present invention relates to a method for printing thick film circuits.

For thick film circuits such as thick film hybrid ICs, mounting electronic components through a printing process is widely practiced, but since the resistance value and capacitance change depending on the thickness of the printed film, it is necessary to control the film thickness to a constant level. be.

If the film thickness is too large, various types of trimming are performed to maintain a constant circuit constant, but if the film thickness is smaller than a predetermined value, trimming cannot be performed and the product will be defective. is printed in advance so that it is larger than the kana. The printing film thickness depends on various conditions during printing, e.g.
Printing pressure during printing (printing squeegee pressure) varies depending on the printing squeegee speed, the distance between the screen (mask) and the printing board (screen distance), etc. Conventionally, after printing, the surface of the thick film circuit element is hardened by drying, and the hardened dry thick film is measured using a stylus roughness meter to control the printing conditions described above. With this conventional stylus measurement method, measurements cannot be made unless it is in a hardened state, so it takes time to dry after printing, and during this time the printing process must be stopped or the printing process must be restarted at the risk of producing defective products. It has the disadvantage that it has to be continued, resulting in poor yield. Furthermore, the conventional stylus-type measurement method has the drawback of damaging the thick film circuit element and degrading the performance of the product. Furthermore, in order to reduce such a risk, it is necessary to increase the thickness of the printing film in advance as described above, which has the drawback of increasing the consumption of printing paste and increasing costs. The purpose of the present invention is to eliminate the above-mentioned conventional drawbacks, and to enable efficient printing of thick film circuits by measuring the film thickness of thick film circuit elements immediately after printing without curing, thereby increasing the production yield of thick film circuits. An object of the present invention is to provide a method for printing thick film circuits that improves the performance and reduces costs.

In order to achieve the above object, the present invention provides a film of a thick film circuit element formed by a surface of a thick film circuit element such as a resistor, a capacitor, a conductive path, etc. printed on a substrate in advance and a surface of a substrate. The thickness is measured by an optical non-contact method, and printing conditions such as squeegee pressure, screen distance, and squeegee speed are adjusted according to the measured film thickness dimension to form a thick film circuit element with a predetermined film thickness on the substrate. The invention is characterized by printing a thick film circuit having the following properties.

In particular, the above-mentioned optical non-contact method projects a fine pattern onto the surface of a thick film circuit element and the surface of a substrate using a projection optical system. The contrast between the projection optical system and the thick film circuit element is detected by the imaging means, and the projection optical system or the thick film circuit test stand is moved up and down so that the signal detected by the imaging means becomes larger. , and the relative distance to the surface of the substrate, and measure the film thickness of the thick film circuit element from these controlled variables. That is, this contrast signal is generated at the focal position of the projection optical system, at the surface of the thick film circuit element, and at the surface of the substrate adjacent to both sides of the thick film circuit element.
At 4 o'clock, the fine pattern is most clearly projected and the contrast signal is maximum (this state is called the in-focus state).
) as the surface of the thick film circuit element and the surface of the substrate shift upward or downward from the focal position, the contrast signal decreases, so the projection optical system detects this contrast signal and increases the contrast signal; By controlling the relative distance between the surface of the thick film circuit element and the surface of the substrate, the final state with the highest contrast signal level can be achieved.
In other words, it becomes a focused state. The amount of movement (amount of vertical fine movement) of the projection optical system or the thick film circuit sample stage in these focused states is detected and stored. Since the shape of the substrate beneath the thick film circuit element is known in advance from these detected amounts (generally, the substrate surface is flat), it is possible to automatically calculate the film thickness of the thick film circuit element. This makes it possible to immediately provide feedback to printing conditions. The present invention will be described in detail below based on embodiments shown in the drawings.

FIG. 1 is a diagram showing a method of printing a thick film circuit according to the present invention.

In FIG. 1, reference numeral 1 denotes an optical non-contact film thickness automatic measuring device for measuring the film thickness of a thick film circuit pattern in an undried state immediately after printing, the details of which will be explained later. 2 is a printing device for thick film circuits, and 24 is a printing head.

21 is the pressure of this printing head during printing (squeegee pressure)
22 is a screen distance control section that controls the distance between the screen and the printing substrate, and 23 is a section that controls the speed of the printing squeegee.

The printed thick film circuit is carried by the transport mechanism 42 to the optical non-contact automatic thick film measuring device 1, loaded onto the measuring device by the sample loading device 19, and is predetermined according to the printing pattern of the thick film circuit. By reading and inputting a recording medium 25 such as an NC tape on which measurement points have been recorded using a reader 26, the film thickness automatic measurement control circuit 18 causes the measurement points to come to the point where the fine pattern is projected by the optical system. The X table 16 and Y table 17 are driven as shown in FIG. , the film thickness is calculated from the measured surface shape.Next, a method for measuring the film thickness of a thick film circuit will be specifically explained based on FIGS. 2 and 3.

FIG. 2 is a diagram showing a schematic configuration of an optical non-contact automatic film thickness measuring device. That is, reference numeral 11 denotes an optical focus detection head, which is equipped with an objective lens 12, and is controlled so that the surface of the sample 13 (thick film circuit) comes to the focal position of the objective lens 12. Reference numeral 14 denotes a sample table on which a thick film circuit is mounted, and this sample table 14 is moved in three directions by a vertical fine movement mechanism 15, an X table 16, and a Y table 17.

The X table 16 and the Y table 17 are used to measure the thick film circuit element 13 a to be measured by the thick film circuit 13 and the alumina substrates 13 b on both sides of the thick film circuit element, based on the contents recorded on the recording medium 25 . It is used to control it so that it comes directly below. As mentioned above, the vertical fine movement mechanism 15 has a thick film circuit element 13 at the focal position of the objective lens 12.
Automatic focus control is performed by making slight movements up and down so that the surface of a and the surface of the alumina substrate 13b are aligned, and at the same time, the amount of this slight movement at each measurement point is stored in a memory.

A method for calculating the film thickness of the thick film circuit element 13a using a logic circuit such as a microcomputer from the amount of slight movement at each measurement point stored in the memory will be described later. FIG. 3 is a diagram showing a specific embodiment for carrying out the above-mentioned automatic focus control.

101 is a semiconductor laser, 102 is a white light source, 103 is 2
periodic fine pattern, 104 is an optical position detector, 105 is 2
A fine pattern contrast detector is composed of a photodiode array arranged in a dimension, 106 and 107 are wavelength selection mirrors, 108 and 109 are wavelength selection filters, 110 is a semi-transparent mirror, and 111 and 112 are lenses.

However, the semiconductor laser 101 and the lens 111 irradiate the surface of the thick film circuit 13 (the surface of the thick film circuit element 13a and the surface of the alumina substrate 13b) obliquely through the objective lens 12. If the surface of the thick film circuit element 13a or the surface of the alumina substrate 13b is located at the focal position of the objective lens 12 (this does not mean the focal length, but means a position where the conditions are such that a good image can be formed), this The light reflected on the surface passes through the objective lens 12 again, and then passes through a semi-transparent mirror 110, a wavelength selection mirror 107 that allows only the laser beam to pass, and a wavelength selection mirror 108 that allows only the laser beam to pass, and is then sent to an optical position detector. 104 is adjusted to be in the center. If the surface of the thick film circuit element 13a or the surface of the alumina substrate 13b is above (or below) the focal point, the reflected light will be directed to the right above (or below) the optical position detector 104.
or left), a signal Ip in FIG. 7 is obtained from the optical position detector 104, and from this signal 1p, the thick film circuit element 13a
It is possible to know where the surface of the alumina substrate 13b or the surface of the alumina substrate 13b is relative to the focal position.

However, if the vertical fine movement mechanism 15 is driven by the film thickness automatic measurement control circuit 18 using the output signal 1p from the detector 104, the surface of the thick film circuit element 13a can be moved almost to the focal point (within a range of about 50 μm). Alternatively, it is possible to position the surface of the alumina substrate 13b. However, in this method, some of the light is transmitted through the thick film circuit element 13a, the alumina substrate 13b, etc., and the reflected light from the vicinity of these surfaces is imaged on the optical position detector 104, so these surfaces can be accurately detected. It is impossible to locate the focal point. Therefore, using a two-period fine pattern 103 shown in FIG. 4, this pattern 103 is illuminated with a white light source 102 and projected onto the surface of the thick film circuit element 13a or the surface of the alumina substrate 13b. An object located at the objective-side focal position of the objective lens 12 (a position under conditions for good image formation) is focused at the position where the two-period fine pattern 103 is arranged and on the imaging surface of the fine pattern contrast detector 105. If the optical system is arranged so that the sample surface is imaged by objective lens 1,
At the second focal position, the two-period fine pattern 103 is clearly projected onto the sample surface, and the image of the projected pattern is again clearly focused on the imaging surface of the fine pattern contrast detector 105 by the objective lens 12. That will happen. However, if the sample surface deviates from the focal position, an unclear pattern, that is, a pattern with low contrast, will be imaged on the imaging surface 105. A method for specifically obtaining the above-mentioned contrast signal will be described next. Figure 4 is the third
It is a detailed view of the two-period fine pattern 103 shown in the figure. In FIG. 4, 103a is a light transmitting part, and 103b and 103c are light shielding parts. The 2-period pattern 103 has a fine period (pitch 2P
) and a coarse pattern with a coarse period (pitch 17P).

The reflected light is projected onto the sample surface and then passes through the objective lens 12.
The image is formed on the imaging surface of the fine pattern contrast detector 105, and the relationship between the light receiving element on this imaging surface and the image is determined by the fifth
As shown in the figure, the arrangement pitch of the light receiving elements 105a constituted by a two-dimensional photodiode array on the imaging surface is set to be % of the pitch 2P of the dense pattern. In addition, each light receiving element 105a is placed in advance at the center of the dense pattern of the two-period pattern 103.
It is arranged and adjusted so that it is located in the center of the From this light receiving element 105a, images are taken out in time series in the pattern change direction of the periodic pattern to be imaged, and information is taken out in parallel at the same time in the direction perpendicular to this direction.
As shown in the figure, two-dimensional pattern information is obtained in parallel and in time series as signals indicated by Sl, S, . . . Sl. The obtained signal is converted into a contrast signal by a contrast detection processing circuit in the automatic film thickness measurement control circuit 18, as shown in FIG. This contrast signal is generated for each of the dense pattern and the coarse pattern, and will be explained in detail using FIG. 6. In FIG. 6, 113 is an adder circuit which calculates the sum of signals in a direction perpendicular to the changing direction of the two-period pattern 103, that is, in the direction in which the pattern does not change (y direction). Therefore, the output of the adder circuit 113 is 1 in time series.
The signal becomes s(t). s(t red subtraction absolute value circuit 114,
115 and delay circuits 116 and 117. The delay circuit 116 holds s(t) for a time ΔTO corresponding to the time to transfer one pitch P of the light receiving element 105a, and then transfers it to the subtraction absolute value circuit 114. Similarly, delay circuit 117
holds s(t) for nΔTO (time to transfer half of the coarse pattern pitch 17P) and transfers it to the subtraction absolute value circuit 115, so the outputs D, (t) and Dn( t) is the following (1) and (
2) Given by Eq. The signals obtained by the subtraction absolute value circuits 114 and 115 are sent to the integration circuits 118 and 119.
If we integrate D1(t) field and Dn(t), we get this integral value,=FOtODl(t)Dt and In=FOtO
Dn(t)Dt becomes the contrast signal of the projected images of the dense pattern and the coarse pattern, and the contrast signal 11 and In have a shape having a maximum value at the focal point as shown in FIG.

Since the optical position detection signal is used to control the area near the in-focus point, first the coarse pattern contrast signal is used to control the in-focus point, and finally the fine pattern contrast signal is used to control the in-focus point. The surface and the surface of the ceramic substrate 13a can be positioned at the focal point of the objective lens 12. The pitch and L of the two-period pattern shown in FIG. 10-50 μM depending on signal 1n,
The density of 10 μm or less is controlled by the dense pattern contrast signal 11. That is, the thick film circuit sample Yl4 is slightly moved in the vertical direction by driving the vertical fine movement mechanism 15 so that the signal 1p obtained from the optical position detector 104 becomes zero level, and is output from the integrating circuit 118. When the signal 1n to be output reaches the level of Inc, this signal 1n
, and slightly move the thick film circuit sample Yl4 in the vertical direction so that this signal 1n becomes a high level. When the signal 11 output from the integrating circuit 114 reaches the level of 11C, this signal 1, After switching to the control mode, the thick film circuit sample Y14 is moved slightly in the vertical direction so that the signal 11 becomes the highest level, and the surface of the thick film circuit element 13b and the surface of the ceramic substrate 13a are brought to the focal point position by the fine pattern. position. Once the focus is reached in this way,
The amount of vertical fine movement of the thick film circuit sample table 14 is stored in a memory (not shown) in the automatic film thickness measurement control circuit 18. 8th
The figure and FIG. 9 show a method of calculating the film thickness of the thick film circuit 13Q from the data values stored in the memory.

That is, the recording medium 25 is read by the reader 26 and the control circuit 18
Thick film circuit elements 1, such as resistors, connected between conductors 13c formed on a ceramic substrate 13a.
The surface of the thick film circuit element 13b and the surface of the ceramic substrate 13a on both sides of the thick film circuit element 13b are moved across the X
The control device 1 measures the surface position as described above at the measurement points indicated by marks.
Store it in the memory in 8. If these measurement points are plotted on the horizontal axis and the amount of vertical fine movement (surface position) is plotted on the vertical axis, as shown in Section I, the surface position (the amount of vertical fine movement) at the measurement point will be as shown by the X mark. Among these X marks, AO, A,, A,, As,
and BO·,B,,B,,B, are the irregularities on the surface of the alumina substrate 13a, and the other portions marked with x are the irregularities on the surface of the thick film circuit element 13b. First, the minimum values (A, and BO) on the left and right sides of the position C (Δ mark), which is the center of the entire measurement point commanded by the recording medium 25 given by the pattern of the thick film circuit 13, are determined, respectively. Select at least three measurement points that are connected to the minimum value and show a low value, and find the vertical fine movement AlTA2T83.

This average value A=? And B0+B1+B2 and B2? is the representative value at the center q measurement point of the three measurement points, connect the left and right representative values A1 and B with a straight line AB, and connect this straight line AB to the ceramic substrate 1.
3a, the thick film circuit element 13 is
Let the distance to each measurement point on the surface of b be the film thickness at each measurement point.

Therefore, in order to provide feedback to the printing conditions of the printing device, it is necessary to determine the average thickness or cross-sectional area of the thick film portion.
The cross-sectional area may be calculated by calculating the cross-sectional area between A3AO above AB. To measure the average film thickness, for example, draw straight lines Ll and L2 at a height t from line AB, and connect L, L2 and the cross-sectional shape (DO and D are connected with a straight line, FO and F1 are connected with a straight line). Find the intersection El, E2, and find the center Cl of El, E2.
, the film thickness at a certain number (for example, 3) of measurement points (marks) on both sides centering on C2 (however, the distance between A2Bl is 15q, .A2
The distance between A1 is 5q. Between H1H2, H2H3, H3H
The distances between 4, H4H, and H5H6 are each q0
) and find this value h1kuraH2)H3? H4TSH,,h6
What is necessary is to calculate the average film thickness H, +H2+H3+H4+H5+H6 h2.

That is, each height h1》H22h3》H4》H5h6 from the line AB to the surface of the thick film circuit element 13b is determined, and these are averaged to determine the thickness of the thick film circuit element 13b. Once the film thickness or cross-sectional area of the printed circuit pattern is measured in this way, this value is transmitted to the printing condition control circuit shown in FIG. 120.

The printing paste forming the printed circuit element 13b is made by mixing the solids (inorganic substances) remaining after firing with a vehicle (consisting of ethyl cellulose, a solvent such as α-terpineol, β-terpionel, tordecanol, etc., and a pigment-based additive). This printing paste has inherent viscosity, and the printing film thickness is determined by the squeegee pressure during printing, P1, the distance between the screen (mask) and the substrate, d, and the squeegee speed υ during printing. As printing is performed many times, the tension on the screen changes and the distance d becomes smaller, and the solvent evaporates and the viscosity increases, so the film thickness immediately after printing can be measured using the method described above. When measured and this data is sent to the printing condition control circuit, the deviation from the predetermined thickness is first calculated, and if this deviation is within the allowable range, printing is continued under the same conditions. If it exceeds the allowable range, first change the squeegee pressure at a predetermined rate of change. If this is done, the screen distance d will be within the allowable range, but once the squeegee pressure reaches a predetermined limit value, the screen distance d will be adjusted next. At this time, only the clean distance d may be adjusted without changing the squeegee pressure, or the clean distance d may be slightly changed and the squeegee pressure P may be changed at the same time. When both the squeegee pressure P and the screen distance d reach predetermined limit values, the printing squeegee speed υ is changed.
By assigning priorities in this way and changing the printing conditions, control is performed to maintain a constant printed film thickness. All printed circuits are transferred to an automatic optical non-contact film thickness measuring device, and representative circuit pattern numerical force points are measured. If these measured values are averaged over several substrates and fed back to the printing conditions, unstable feedback due to variations in individual printed film thicknesses can be avoided, which is highly effective. Furthermore, if the printing apparatus is operating stably, it is not necessary to measure all the circuit boards, but it is also possible to measure samples at a constant sampling rate and perform feedpacking to the printing conditions. In the above embodiment, the automatic focus detection method uses three types of control signals: a contrast signal of a two-period fine pattern and a semiconductor laser optical position detection signal. The object of the present invention can be achieved to some extent by using only the position detection signal or by using only the two-period fine pattern contrast signal.

As explained above, according to the present invention, it is possible to perform high-precision automatic measurement of the print film thickness in the wet state immediately after printing, which was previously impossible in the printed circuit manufacturing process, using an optical non-contact method. This feedback makes it possible to maintain a constant printing film thickness, which improves yield and eliminates material waste, which is extremely effective in reducing costs and improving performance.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram showing a printing device according to the thick film circuit printing method of the present invention, and FIG. 2 is a schematic diagram showing an optical non-contact film thickness automatic measuring device according to the thick film circuit printing method of the present invention. 3 is an enlarged view of the automatic focus detection head of the device shown in FIG. 2, and FIG. 4 is a diagram showing the two-period pattern incorporated in the automatic focus detection head shown in FIG. 3. , FIG. 5 is a diagram showing the imaging state of this two-period pattern on the fine pattern contrast detector, and FIG. 6 is a diagram showing the contrast detection circuit in the film thickness automatic measurement control circuit shown in FIGS. 2 and 3. FIG. 7 is a diagram showing changes in the signal output from the optical position detector and the contrast detection signal output from the contrast detection circuit according to the deviation from the in-focus position, and FIG. 8 is a diagram according to the present invention. FIG. 9 is a perspective view showing an example of a thick film circuit; FIG. 9 is a diagram for explaining a method for determining the film thickness and cross-sectional area from the amount of vertical movement at each measurement point of the thick film circuit shown in FIG. 8; . Explanation of symbols, 1... Optical non-contact automatic film thickness measurement, 2... Printing device, 3... Drying device,
11...Rolling focus detection head, 12...
Objective lens, 13...Thick film circuit, 13a...
...Ceramic substrate, 13b...Thick film circuit element, 15...Vertical fine movement mechanism, 16...
X table, 17... Y table, 103...
. . . 2 period fine pattern, 104 . . . optical position detector, 105 . . . fine pattern contrast detector.

Claims (1)

[Claims] 1. A projection optical system projects a fine pattern onto the surface of a thick film circuit element printed on a substrate in advance and the surface of a substrate, and the contrast of these projected patterns is detected by an imaging means. The relative distances between the projection optical system and the surface of the thick film circuit element and the surface of the substrate are controlled so that the contrast signal detected by the A thick film circuit element with a predetermined film thickness is formed on the substrate by adjusting the printing conditions according to the film thickness dimension measured by the film thickness measurement process using an optical non-contact method. A method for printing a thick film circuit, comprising: a film thickness adjustment printing step of printing a thick film circuit having the following steps: 2 In the film thickness measurement step, the fine pattern is
The relative distance is roughly controlled by a contrast signal of a coarse period pattern detected by the imaging means, and the relative distance is roughly controlled by a contrast signal of a fine period pattern detected by the imaging means. 2. The thick film circuit printing method according to claim 1, wherein the relative distance is finely controlled. 3 In the film thickness measurement step, the surface of the thick film circuit element or the surface of the substrate is obliquely irradiated with highly directing light, and the light reflected from the surface of the thick film circuit or the surface of the substrate is formed into an image. The thick film according to claim 1, further comprising the step of detecting the position by an imaging means and roughly controlling the relative distance based on a position signal detected by the imaging means. How to print circuits.