Method for joining metal or conductive micro-columnar pins to electrode pads of a workpiece

Abstract

To provide a method for joining a workpiece to an electrode pad portion, which uses a simple cylindrical ultra-small columnar pin to reduce the manufacturing cost of the pin, can be mounted efficiently, and further can firmly join the ultra-small columnar pin without tilting it. [Solution] The method involves activating the flux contained in the printed solder paste at a temperature where the flux begins to become active, liquefy, and volatilize, but not melt the solder particles, thereby homogenizing the particles of the solder paste, which may be uneven in height. The solder paste is then allowed to cool naturally at room temperature in this state. Flux is then printed again on top of this. Metal or conductive micro-column pins 5 are placed on top of the printed flux through a metal mask. The metal mask is then peeled off from the electrode pads. Finally, the workpiece 2 with the metal or conductive micro-column pins mounted is reflowed at high temperature to melt the solder particles and bond the metal or conductive micro-column pins to the workpiece's electrode pads.

Description

[Technical Field]

[0001] The present invention relates to a method for joining metal or conductive minute columnar pins, known as Cu-Pins, Cu-Pillars, Cu-Posts, Cu-Columns, etc., to electrode pads of workpieces such as semiconductor wafers and printed circuit boards. [Background technology]

[0002] There is a process for mounting metal or conductive micro-columnar pins such as Cu-Pins on the electrode pads of workpieces such as semiconductor wafers and printed circuit boards, such as Package-on-Package (POP).

[0003] In this process, it is desirable to bond the metal or conductive micro-columnar pins as vertically as possible to the electrode pads of the workpiece. However, the metal or conductive micro-columnar pins are unstable due to their straight shape and extremely small diameter, and tend to tilt when the solder melts during reflow (see Figure 1).

[0004] In consideration of this point, some metal or conductive micro-pillar pins have a flange-like protruding portion with a diameter larger than the main body integrally formed on the end face of the pin that joins with the electrode pad. However, in this case, the manufacturing cost of the micro-pillar pins is high, and when mounting the micro-pillar pins on the electrode pad of the workpiece, the protruding portion gets in the way, making it impossible to perform bulk mounting using a metal mask. In addition, the protruding portion creates a problem of limitations when the pitch is fine. Summary of the Invention [Problem to be solved by the invention]

[0005] The present invention has been made in consideration of the above points, and aims to provide a method for joining a metallic or conductive tiny pillar pin to an electrode pad of a workpiece, which does not require the provision of a flange-like protruding portion on one end of the main body as in the prior art, but uses a simple cylindrical tiny pillar pin, which can be stably held on the electrode pad of the workpiece without tilting, and during reflow a fillet is formed, which prevents the tiny pillar pin from tilting and creates a strong bond. [Means for solving the problem]

[0006] The gist of the present invention is as follows: A method for joining metal or conductive micro-columnar pins to electrode pads of a workpiece such as a semiconductor wafer or a printed circuit board, comprising the following steps: The method for joining metal or conductive minute columnar pins to electrode pads of a workpiece comprises the steps of a. to h. a. A solder paste consisting of solder particles and flux is applied to the electrode pad portion. A process of applying by printing. b. Use an oven or similar device to heat the flux to a temperature where it becomes activated, liquefied, and volatilized. At the same time, the solder particles printed on the electrode pads are applied at a temperature at which the solder particles do not melt. This is the process of activating the flux contained in the solder paste. c. The electrode pad portion is printed The flux contained in the solder paste is liquefied. The aforementioned Solder paste with uneven height applied to the electrode pad To Leveling, The flux contained in the solder paste is volatilized on the electrode pad portion, and the remaining solder A process for flattening particles. d. In this state, at room temperature Under Natural cooling process. e. The solder particles are again applied to the flattened surface of the electrode pad portion. Flux, By printing in an amount sufficient to cover the surface of the solder particles, the minute pillar pins can be fixed on the electrode pads. The process of doing this. f. Above the workpiece, through an opening in a metal mask at a height that does not contact the flux on the surface of the solder particles of the electrode pad portion, The process of erecting tiny columnar pins. g. After the step of erecting the micro pillar pins is completed, Metal mask as work Peeling from The process of doing this. h. After the step of peeling the metal mask from the workpiece is completed, By reflowing the workpiece with the ultra-small columnar pins at high temperature, The electrode pad portion is planarized. The solder particles are melted to form the micro-pillar pins. and before A step of bonding to the electrode pad portion. [Effects of the Invention]

[0007] The present invention provides A method for joining metal or conductive micro-columnar pins to electrode pads of a workpiece such as a semiconductor wafer or a printed circuit board, comprising: a. applying a solder paste made of solder particles and flux to the electrode pad portion by printing; b. activating the flux contained in the solder paste printed on the electrode pad portion using an oven or the like at a temperature at which the flux is activated, begins to liquefy, and volatilizes, but at a temperature at which the solder particles do not melt; c. A process of leveling the unevenly applied solder paste on the electrode pad portion by liquefying the flux contained in the solder paste printed on the electrode pad portion, and flattening the remaining solder particles by volatilizing the flux contained in the solder paste on the electrode pad portion; d. A process of cooling naturally at room temperature in this state; e. A process of printing flux again on the flattened surfaces of the solder particles on the electrode pad portion in an amount sufficient to cover the surfaces of the solder particles, thereby making the tiny pillar pins fixable on the electrode pad portion; f. A step of erecting the minute pillar pins above the workpiece through openings in a metal mask at a height such that the pins do not come into contact with the flux on the surfaces of the solder particles of the electrode pads; g. After the step of erecting the minute columnar pins is completed, the metal mask is peeled off from the workpiece; h. After the step of peeling the metal mask from the workpiece is completed, the workpiece on which the tiny pillar pins are mounted is reflowed at a high temperature to melt the solder particles that have been flattened on the electrode pads, thereby joining the tiny pillar pins to the electrode pads, thereby providing the following effects: (1) Since the solder particles are flattened on the electrode pad portion, when an extremely thin cylindrical pin is set up on the electrode pad portion, the pin is less likely to fall over. (2) Furthermore, flux is printed on the surface of the electrode pad portion where the solder particles are flattened, in an amount sufficient to cover the surface of the solder particles, as an adhesive for the tiny columnar pins, so that the tiny columnar pins can be mounted and fixed in a vertically standing position. This allows the tiny columnar pins to be temporarily fixed without falling over when standing. (3) Furthermore, flux is printed on the flattened surface of the solder particles on the electrode pad portion so as to cover the surface of the solder particles. This allows the solder to form good fillets during subsequent reflow without being affected by surface oxidation of the tiny columnar pins, resulting in a strong bond without tilting the tiny columnar pins. (4) Therefore, unlike the conventional method, it is not necessary to provide a flange-like protruding portion at one end of the main body of the extremely small columnar pin, and a simple cylindrical pin can be used, thereby reducing the manufacturing cost of the extremely small columnar pin. (5) Furthermore, the minute columnar pin can be temporarily fixed stably onto the electrode pad of the workpiece without tilting, and a fillet is formed during reflow, making it possible to create a strong bond without tilting the minute columnar pin in a shorter time than conventional methods. (6) Furthermore, since the micro-column pins do not have a flange-like protruding portion on one end of the main body as in the conventional case, it is possible to mount the micro-column pins all at once using a metal mask, and the micro-column pins can be mounted efficiently. (7) In addition, even if the arrangement pitch of the electrode pad portions becomes finer, it can cope with this more easily than conventional devices. [Brief explanation of the drawings]

[0008] [Figure 1] 10 is an explanatory diagram of a conventional metal or conductive micro-columnar pin mounted on an electrode pad portion of a workpiece. FIG. [Figure 2] FIG. 10 is an explanatory diagram of a method for joining a metal or conductive tiny pillar pin to an electrode pad portion of a workpiece according to an embodiment of the present invention, showing the state in which solder paste has been applied by printing or transfer. [Figure 3] This indicates the state in which the flux becomes activated by low-temperature heating, liquefies, and then evaporates, resulting in the solder becoming flat. [Figure 4] The figure shows a state in which flux, which is an adhesive agent for mounting metal or conductive micro-pillar pins, is applied onto the solder layer. [Figure 5] This shows a state in which metal or conductive micro-columnar pins are mounted vertically on the electrode pads of the workpiece via a metal mask. [Figure 6]This shows the state in which the metal mask has been peeled off from the workpiece after metal or conductive micro-columnar pins have been mounted. [Figure 7] The solder particles are melted by reflowing, and the solder is joined to the metal or conductive pin in a fillet shape. [Figure 8] 6 is a diagram showing an example of a metal mask according to an embodiment different from the metal mask shown in FIG. 5. [Figure 9] FIG. 2 is a diagram showing the metal mask in use. DETAILED DESCRIPTION OF THE INVENTION

[0009] The embodiment of the present invention shown in FIGS. 2 to 9 will be described below.

[0010] In the figure, 1 is a jig that sucks the workpiece with a vacuum pump. 2 is the workpiece, and 3 is its electrode pad. 4 is solder paste applied by printing or transfer. 5 is a metal or conductive micro-columnar pin that is mounted on the electrode pad of the workpiece.

[0011] 6 is a solder particle that is flattened after the flux of solder paste applied by printing or transfer is activated and begins to liquefy and volatilize when heated in an oven, etc. 7 is a flux that acts as an adhesive for metal or conductive micro-columnar pins applied by printing or transfer, and 8 is a metal mask.

[0012] Reference numeral 9 denotes solder. The solder 9 is shown in a state where the solder particles have melted by reflow and are joined in a fillet shape to the electrode pads of the workpiece 2 and the metal or conductive micro-columnar pins 5. Reference numeral 8a denotes a metal mask according to another embodiment of the metal mask 8.

[0013] FIG. 8 shows the metal mask of the other embodiment, and FIG. 9 shows it in use. In the figure, 5 denotes a metal or conductive minute columnar pin, and 8a denotes a metal mask.

[0014] In the same figure, the opening 10 is composed of a holding portion 10A with an inner diameter slightly larger than the diameter of the metal or conductive tiny columnar pin 5, and an introduction guide portion 10B that is continuous with the upper part of the holding portion 10A, has an inner diameter larger than that of the holding portion 10A, and is straight from the upper end to the lower end.

[0015] Furthermore, the height H2 of the introduction guide portion 10B is about 1 / 3 of the length of the metal or conductive tiny columnar pin, and the inner diameter D2 of the introduction guide portion 10B is the inner diameter D1 of the holding portion 10A plus about 1 / 2 of the length of the metal or conductive tiny columnar pin 5.

[0016] In addition, a rib 11 is provided on the underside of the metal mask 8a. The rib 11 has a height H3. This height H3 keeps the underside of the metal mask 8a from coming into contact with the flux applied to the electrode pads. The rib 11 is formed to surround a group of electrode pads formed on the workpiece. The provision of such a rib 11 prevents the flux applied to the electrode pads of the workpiece from adhering to the underside of the metal mask 8a, thereby eliminating the need to clean the metal mask 8a. An appropriate gap is provided between the inner surface of the rib 11 and the electrode pads to prevent contact.

[0017] Next Previous The method of using the metal mask 8a will now be described. The metal mask 8a is With the above-mentioned configuration, the opening 10 ,very The holding portion 10A has an inner diameter slightly larger than the diameter of the small columnar pin 5, and the introduction guide portion 10B is continuous with the upper portion of the holding portion 10A, has an inner diameter larger than that of the holding portion 10A, and is straight from the upper end to the lower end. Side opening area , i.e. , applicable The extremely small columnar pin 5 is inserted The introduction guide part 10B The opening area on the inlet side has been enlarged , applicable One end of the very small columnar pin 5 in the length direction enters the opening and falls Easy In addition, the extremely small columnar pin 5 is Even if it's completely overturned , applicable The minute columnar pin 5 loses balance above the opening 10, and one end of the pin in the length direction falls into the opening 10. 10B is straight from the top to the bottom, and is the introduction guide. 10B and holding part 10A This is because it is stepped. , the very small columnar pin 5 Once it starts to tilt, it slides down immediately. Easy , which can be dropped reliably.

[0018] Furthermore, the metallic or conductive tiny pillar pin 5 that has fallen into the holder 10A can be set up vertically at the center of the electrode pad of the workpiece because the inner diameter of the holder 10A is slightly larger than the diameter of the metallic or conductive tiny pillar pin 5. The metal mask 8a having the openings 10 according to this embodiment is manufactured by adding a plating process.

[0019] Also, As shown in FIG. 8, the metal mask 8a has a high The rib has a height H3 and surrounds a group of electrode pads formed on the workpiece. 11 This allows the electrode pads of the workpiece to be again Printed and coated Flux is metal mask 8a This prevents adhesion to the underside of the metal mask. 8a This can save the trouble of cleaning the

[0020] A method for mounting a metal or conductive micro-columnar pin on an electrode pad of a workpiece according to the present invention will be described below. a. A process in which an adhesive such as solder paste is applied by printing to the electrode pads of workpieces such as semiconductor wafers and printed circuit boards. b. A process in which the flux contained in the solder paste is activated using an oven or other device at a temperature where the flux becomes active, liquefies, and evaporates. In this embodiment, this temperature is set to 100° C. This is because if reflow is performed at a high temperature, the workpiece may expand and contract, causing it to no longer match the positions of the holes in the metal mask. c. A process in which the flux contained in the printed solder paste is liquefied to level out the uneven height of the solder paste particles that have been applied to the electrode pads, thereby flattening the solder paste particles. Figure 3 shows the state in which the evenly flattened solder paste remains on the electrode pad after the flux has evaporated, with evenly flattened solder particles remaining on the electrode pad. d. A process of cooling the mixture at room temperature in this state. Here, wait for the temperature to drop naturally at room temperature. e. A process in which flux is printed again as an adhesive for the metal or conductive micro-pillar pins to mount them on the electrode pad portion in a state in which the solder particles have not melted but have been flattened and remain on the electrode pad portion. At this time, it is desirable that the amount of flux be just enough to cover the electrode pads. This state is shown in Figure 4. f. A process of erecting metal or conductive micro-columnar pins through a metal mask onto the electrode pads of the workpiece on which the flux has been printed in the process e. At this time, the mounted metal or conductive micro-columnar pin rests on the solder that has been flattened in advance, so it can stand upright without being affected by the unevenness of the solder-coated surface (see Figure 5). g. After the mounting of the metal or conductive micro-columnar pins is completed, the metal mask is peeled off from the electrode pad portion of the workpiece. This state is shown in Figure 6. h. After peeling off the metal mask, the workpiece on which the metal or conductive micro-pillar pins are mounted is reflowed at high temperature to melt the solder particles, thereby joining the metal or conductive micro-pillar pins to the electrode pads of the workpiece. This state is shown in Figure 7. At this time, it can be seen that the solder melted by surface tension due to reflow heating is joined to the metal or conductive micro-columnar pin in a fillet shape. The temperature at this time is 220°C in this embodiment. The metal mask used in step f can be the one shown in Figure 5, or the ones shown in Figures 8 and 9. This was previously proposed by the applicant and has already been patented as Japanese Patent No. 7165835. By using this metal mask, it is possible to more reliably position the metal or conductive micro-columnar pins upright on the solder.

[0021] Therefore, unlike the conventional method, it is not necessary to provide a flange-like protruding portion on one end of the main body, and simple cylindrical micro-pillar pins 5 can be used, thereby reducing the manufacturing cost of the micro-pillar pins. Furthermore, the micro-pillar pins 5 can be temporarily fixed stably without tilting onto the electrode pads 3 of the printed circuit board 1, and a fillet 9 is formed during reflow, resulting in a strong bond without tilting of the micro-pillar pins. Furthermore, since the micro-pillar pins 5 do not have a flange-like protruding portion on one end of the main body, as is the case with the conventional method, they can be mounted all at once using metal masks 8, 8a, allowing for efficient mounting. Furthermore, even if the pitch becomes finer, this method can accommodate this more easily than conventional methods. [Explanation of symbols]

[0022] 1 Jig 2 Work 3 Electrode pad section 4. Solder paste 5 Metal or conductive micro-column pins 6 Solder particles 7. Flux as an adhesive 8 Metal Mask 8a Metal Mask 9 Solder fillet 10 Opening 10A holding part 10B Introduction Guide

Claims

[Claim 1] A method for joining metal or conductive micro-columnar pins to electrode pads of a workpiece such as a semiconductor wafer or a printed circuit board, comprising: applying a solder paste made of solder particles and flux to the electrode pad portion by printing; a step of activating the flux contained in the solder paste printed on the electrode pad portion using an oven or the like at a temperature at which the flux is activated, begins to liquefy, and volatilizes, but at a temperature at which the solder particles do not melt; a step of leveling the unevenly applied solder paste on the electrode pad portion by liquefying the flux contained in the solder paste printed on the electrode pad portion, and flattening the remaining solder particles by volatilizing the flux contained in the solder paste on the electrode pad portion; A process of cooling the mixture naturally at room temperature in this state; a step of printing flux again on the flattened surfaces of the solder particles on the electrode pad portion in an amount sufficient to cover the surfaces of the solder particles, thereby making the minute pillar pins fixable on the electrode pad portion; a step of erecting the minute pillar pins above the workpiece through openings in a metal mask at a height such that the pins do not come into contact with the flux on the surfaces of the solder particles of the electrode pads; a step of peeling the metal mask from the workpiece after the step of erecting the extremely small columnar pins is completed; a step of, after the step of peeling the metal mask from the workpiece, reflowing the workpiece on which the tiny pillar pins are mounted at a high temperature to melt the solder particles flattened on the electrode pads, thereby joining the tiny pillar pins to the electrode pads; 1. A method for joining a metal or conductive micro-columnar pin to an electrode pad portion of a workpiece, comprising:

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