Via Adhesive Mounting

Abstract

A method for attaching two electronic circuit boards, e.g., a test PCB and a space transformer, includes the steps of tack welding a resin prepreg and a Mylar film to the test PCB, laser drilling via holes in the resin prepreg and the Mylar film such that the holes align with the connection / capture pads on the test PCB on one side of the resin prepreg and align with the connection capture pads on the space transformer (after attachment) on the other side of the resin prepreg, filling the via holes with sinter paste, applying a pressure process to remove air, bubbles and voids from the sinter paste, removing the Mylar film, and attaching the space transformer to the resin prepreg using a lamination press cycle.

Description

[Technical field]

[0001] The present invention relates generally to an apparatus and method for mounting a space transformer to a PCB (printed circuit board). [Background technology]

[0002] In the current state of the art, space transformers are connected to the test PCB (or other PCBs) via an interposer (spring contact array), mechanically bolted to the PCB, or attached by direct soldering, but these attachment / connection methods suffer from significant drawbacks.

[0003] Interposer technology has non-uniform planarity and high resistive via values.

[0004] Soldering is done after PCB assembly, when the expensive components are already on the board. Soldering is difficult and prone to failure, which can damage / destroy the expensive components and render them unusable. Also, it is difficult to guarantee planarity between the PCB and the space transformer. Furthermore, soldering does not allow for recess mounting on the PCB.

[0005] What is needed is an improved method for attaching a space transformer to a PCB, and an improved space transformer PCB device. Summary of the Invention

[0006] Disclosure of the Invention A method for attaching two electronic circuit boards, e.g., a test PCB and a space transformer, includes the steps of tack welding a resin prepreg and a Mylar film to the test PCB, laser drilling via holes in the resin prepreg and the Mylar film such that the holes align with the connection / capture pads on the test PCB on one side of the resin prepreg and align with the connection capture pads on the space transformer (after attachment) on the other side of the resin prepreg, filling the via holes with sinter paste, applying a pressure process to remove air, bubbles and voids from the sinter paste, removing the Mylar film, and attaching the space transformer to the resin prepreg using a lamination press cycle.

[0007] The features and advantages of the present invention will become apparent from consideration of the following detailed description, taken in conjunction with the accompanying drawings. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 illustrates an exemplary test PCB. [Diagram 2] FIG. 1 shows a resin prepreg attached to a test PCB. [Diagram 3] FIG. 1 shows resin prepreg and Mylar film attached to a test PCB. [Figure 4] FIG. 13 shows via holes through prepreg and mylar film attached to a test PCB. [Diagram 5] FIG. 2 shows via holes filled with sintering paste. [Figure 6] FIG. 1 shows the test PCB after the Mylar film has been removed. [Figure 7] FIG. 1 shows the test PCB (including resin prepreg, mylar film, and holes filled with sinter paste) before attachment to the space transformer. [Figure 8]FIG. 1 shows the test PCB (including resin prepreg, mylar film, and holes filled with sinter paste) after mounting to the space transformer. [Figure 9] 1 is a flowchart of an exemplary method for attaching a space transformer to a test PCB. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] A system and method for attaching a space translator to a test PCB is disclosed.

[0010] Description of symbols in the drawings

[0011] [Table 1]

[0012] The process for attaching the space transformer to the test PCB may include the processes disclosed below.

[0013] In this disclosure, the abbreviation "mm" is used for millimeters.

[0014] FIG. 9 is a flow chart of an exemplary method for attaching a space transformer to a test PCB.

[0015] In step 910, the resin prepreg and mylar layer / film may be tack welded to the test PCB. FIG. 1 shows the test PCB including pads 110a-n. In one embodiment, the resin prepreg may be an uncured epoxy with woven glass, e.g., FR4 material prepreg. In some embodiments, different prepregs may be used, e.g., prepregs from Rogers Corporation. The thickness of the prepreg and the resin content in the prepreg may be important parameters. Using a prepreg with too much resin content increases the chance of failure due to possible resin flow during the press cycle (discussed below). Too much resin flow may cause the resin to shift / flow and cause the sinter paste to fall out or become misaligned. In one embodiment, a resin content of 70% by weight for a single layer of 1067 prepreg (2.5 mm thick) is a good thickness and sufficient but not too much resin content.

[0016] An advantage of a thinner prepreg may be that it is easier to fill with sinter paste as described herein below.

[0017] FIG. 2 shows a resin prepreg 120 tack welded to a test PCB 105 .

[0018] A sheet / layer / film of Mylar 130 may be applied on top of the prepreg, for example by tack welding, as shown in FIG. 3. The Mylar layer may prevent the sintering paste (described later in this specification) from bleeding onto the prepreg. In one embodiment, a 1 mm Mylar sheet / film may be used. Increasing the thickness of the Mylar may cause failure, as a thicker Mylar will increase the sintering paste after the Mylar is removed, which will cause shorts. In general, a film or layer may be needed to prevent bleeding of the sintering paste, and in one embodiment, this may be a Mylar film.

[0019] In one embodiment, the prepreg 120 and mylar film 130 may be tack welded to the test PCB 105 using a mylar bag and a vacuum laminator at 225 degrees Fahrenheit. Other materials, temperatures and / or procedures may be used to tack weld or attach the prepreg 120 and mylar 130 to the test PCB 105 as understood in the art.

[0020] As shown in FIG. 4, in step 920, vias 140a-n may be laser drilled through resin prepreg layer 120 and mylar layer 130 at locations for electrical connection between the test PCB and the space transformer. In one embodiment, vias 140a-n may be laser drilled using an FR4 laser drilling recipe. The diameter of the laser drilled holes may be 6 mils for an 8 mil diameter capture pad. Generally, the diameter of the laser drill is smaller than the diameter of the capture pads 110a-n so that the laser drill does not "drop" the capture pads.

[0021] 5, in step 930, the drilled holes / vias 140a-n may be filled with sintering paste 150. In one embodiment, the sintering paste 150 may be applied by screen table printing using a squeegee application. In general, many different sintering pastes may be used and may be applied in a variety of ways as known in the art.

[0022] In step 940, the test PCB (including the resin prepreg, the drilled holes, and the sinter paste in the drilled holes) is processed in a pressurized oven to remove air pockets from the via holes. A pressurized oven may be used, but heating may not be required. The pressure may remove the air pockets from the bottom of the via holes by itself (i.e., without heat). In one embodiment, a pressure of 8 bar may be used. Additionally, the pressure may compress the sinter paste into the pads.

[0023] In one embodiment, the pressure oven may be a pressure / vacuum oven (although the temperature characteristics of the oven are not used). A 30 minute cycle may be used for the vacuum and pressure cycle. The vacuum cycle may be 5 minutes. The pressure cycle may be 8 bar pressure for 20 minutes. The cycle may be completed in 5 minutes to degas the chamber. The vacuum cycle may include sucking air and bubbles from the sinter paste and may suck air and gas from the chamber. The pressure / compression cycle may compress the sinter paste and force air out of the sinter paste.

[0024] In one embodiment, the pressure oven is operated at a pressure of 8 bar for 20 minutes.

[0025] Other parameters may be used so long as the air pockets are removed or substantially removed from the via holes. In step 950, a decision may be made regarding optionally adding additional sinter paste to the laser drilled holes to ensure that the holes are adequately filled. This additional filling with sinter paste is only necessary if the holes are not adequately filled. If a decision is made to add additional sinter paste, processing returns to step 930 to add sinter paste and process in a pressurized oven in step 940.

[0026] If it is determined in step 950 not to add additional sinter paste, the test PCB may optionally be inspected for voids and / or incomplete filling in step 960. If voids, incomplete filling and / or other problems are found, steps 130-160 may be repeated.

[0027] As shown in FIG. 6, in step 965, the Mylar film 130 may be removed. In one embodiment, the Mylar film 130 may be removed by heating, for example, in a conventional oven to about 160 degrees Fahrenheit. After heating, the Mylar film 130 may be removed by carefully pulling it away from the resin prepreg. It may be beneficial to pull carefully with both hands, taking care not to remove the sinter paste from the vias. Depending on the properties of the particular Mylar film or other films used, the specific removal parameters or procedures may vary.

[0028] In step 970, the space transformer 160 is attached to the test PCB 105 using a lamination press cycle. Figure 7 shows the space transformer 160 (including pads 170a-n), the test PCB 105, the resin prepreg layer 120, and the sinter paste 150 prior to the lamination press cycle. Figure 8 shows the components and layers after the lamination press cycle.

[0029] The lamination press cycle cures the prepreg 120 and the sinter paste 150. Many lamination press techniques, methods and / or tools are known in the art. Generally, the lamination press cycle uses a combination of pressure and temperature. In one embodiment, the pressure may be set at 450 psi and the temperature ramp pattern may be 180, 195, 300, 365 degrees Fahrenheit, with the temperature maintained at 365 degrees Fahrenheit for 240 minutes. Generally, one skilled in the art can adjust, modify and / or tune the parameters of the lamination press cycle. Additionally, the particular prepreg used may have specific lamination cycle parameters.

[0030] The attachment methods described herein may have several advantages. One advantage is that attachment occurs during the PCB manufacturing process, thereby avoiding damage to components that may be present on the PCB after some or all of the PCB manufacturing is completed. Another advantage is that the space transformer may be attached to the PCB such that it is recessed relative to, and in some cases flush with, the PCB surface.

[0031] Although this disclosure focuses on attaching a space transformer to a PCB, the methods, techniques, techniques, and modifications disclosed herein apply equally to attaching a PCB to a PCB, or attaching a space transformer to a space transformer. [Industrial Applicability]

[0032] The invention disclosed herein is applicable at least to manufacturing instruments and devices for testing electronic consumer devices and other electronic devices.

Claims

1. 1. A method for attaching a first electronic circuit board to a second electronic circuit board, comprising: Fixing a resin prepreg to a mounting side of the first electronic circuit board; creating holes through the resin prepreg at locations of electrical connections on the first electronic circuit board; filling the holes with sintering paste; Pressurizing the first electronic circuit board (together with the resin prepreg and the sintering paste); attaching a mounting side of the second electronics board to a side of the resin prepreg opposite the first electronics board using a lamination press cycle such that electrical connections on the second electronics board are aligned with the sinter paste in the holes; A method comprising:

2. applying a mylar layer to the resin prepreg on an opposite side of the first electronic circuit board after the fixing step and before the creating step; removing the Mylar layer from the resin prepreg after the pressurizing step and prior to the lamination press cycle; The method of claim 1 further comprising:

3. The method of claim 2 , wherein the mylar layer comprises a mylar sheet having a thickness of about 1 mm.

4. The method of claim 1 , wherein the step of fastening the resin prepreg to a mounting side of the first electronic circuit board comprises the step of tack welding the resin prepreg to the mounting side of the first electronic circuit board.

5. The method of claim 1 , wherein the step of creating a hole comprises laser drilling a hole.

6. The method of claim 5 , wherein the step of creating a hole comprises laser drilling a hole having a diameter of about 6 mm.

7. The method of claim 1 , wherein the step of pressure treating the first electronic circuit board includes a vacuum cycle and a pressure cycle.

8. 8. The method of claim 7, wherein the pressure cycle is at about 8 bar pressure for about 20 minutes.

9. After the step of pressurizing and before the step of using a lamination press cycle, adding additional sinter paste to the holes; Pressurizing the first electronic circuit board (together with the resin prepreg and sintering paste); The method of claim 1 further comprising:

10. 10. The method of claim 9, further comprising the step of determining that the holes are not sufficiently filled with sintering paste prior to the step of adding additional sintering paste to the holes.

11. The method of claim 1 , wherein the resin prepreg is an uncured epoxy containing woven glass cloth.

12. 10. The method of claim 1, wherein the resin prepreg is about 2.5 mm thick and has a resin content of about 70% by weight.

13. The method of claim 1 , wherein the step of pressure treating comprises using a pressure / vacuum oven.

14. The method of claim 1 , wherein the first electronic circuit board is a test PCB.

15. The method of claim 1 , wherein the second electronic circuit board is a space transformer.

16. An electronic circuit component, A first electronic circuit board; A second electronic circuit board; a resin prepreg layer attached to a first side relative to a mounting side of the first electronic circuit board and attached to a second side relative to a mounting side of the second electronic circuit board; via holes filled with sinter paste extending through the resin prepreg layers and aligned with first electrical connections of the first electronic circuit board and second electrical connections on the second electronic circuit board; An electronic circuit component comprising:

17. 17. The electronic circuit component of claim 16, wherein the first electronic circuit board is a test PCB.

18. The electronic circuit component of claim 16 , wherein the second electronic circuit board is a space transformer.

19. The method of claim 16 , wherein the resin prepreg is an uncured epoxy containing woven glass cloth.

20. 17. The method of claim 16, wherein the resin prepreg is about 2.5 mm thick and has a resin content of about 70% by weight.

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