A wiring substrate and a manufacturing method for mounting electronic parts such as an IC are provided. In particular, a wiring substrate configured to mount a low-k semiconductor with a particularly low effective permittivity, a switching element, a power system semiconductor element, or the like is provided.
Japanese Unexamined Patent Application Publication No. 2004-228403 describes a switching power device that is reduced in size and thickness and that prevents noise that is caused when a switching element is switched on from affecting the control IC. This document describes that an electrode on the back surface of a power semiconductor element is connected and fixed to a conductor pattern of an insulation substrate. A wiring substrate is disposed in a position opposite to the insulation substrate. A wiring pattern formed in the surface of the wiring substrate opposite to the insulation substrate and an electrode in the upper surface of the power semiconductor element are connected through an electrically conductive post. For conventional semiconductor-mounting substrates, penetrating holes are opened on both surfaces of the substrate and, by inserting a copper post, an electrical connection between the copper post and the conductors of the double-sided substrate are established with the use of an electrically conductive adhesive.
In one exemplary aspect, a wiring substrate for mounting electronic parts is provided. The wiring substrate includes a substrate that includes a first surface, a second surface, and a plurality of through-holes that extend through the substrate from the first surface to the second surface so as to define a plurality of inner walls respectively. The wiring substrate further includes an external conductor formed on at least one of the first surface or the second surface of the substrate. A through-hole conductor is formed on one of the plurality of inner walls of the through-holes so as to define a through-hole conductor space and so as to be electrically connected to the external conductor. Also included is a conductive post having first and second post ends, the first post end being positioned in the through-hole conductor space defined by the through-hole conductor such that the first post end is in contact with and is electrically connected to the through-hole conductor, and the second post end is projecting out of the conductor space.
A manufacturing method of a wiring substrate is provided in another exemplary aspect. The method includes forming a through-hole conductor on an inner wall of a through-hole that has been formed in a substrate. A column-shaped projection part is formed by punching the column-shaped projection part out of a conductive base material such that the column-shaped projection part remains connected to the base material. A position of the projection part and a through-hole opening defined by the through-hole conductor of the substrate are matched. A column-shaped post is formed by punching out the column-shaped projection part from the base material while simultaneously pressing the column-shaped post into the through-hole opening defined by the through-hole conductor of the substrate. An end part of the column-shaped post that has been pressed into the through-hole opening defined by the through-hole conductor is solder-joined to the through-hole conductor.
A more complete appreciation of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:
A wiring substrate to mount electronic parts such as semiconductor elements must be durable against repetitive actions and repetitive temperature volatilities and must stably maintain electrical connections and insulation as well as support for parts. Circuits handling large power capacities, such as a switching power supply or a semiconductor module including a power semiconductor element (e.g. an IGBT (Insulated Gate Bipolar Transistor)) must be especially durable to high heat-discharging properties and repetitive heat cycles. Furthermore, along with the decreasing size of devices, there is a high demand for the prevention of malfunctions caused by noise by reducing such generated noise.
The switching power device described above with respect to Japanese Unexamined Patent Application Publication No. 2004-228403 includes several problems. In the described structure, the conductor of the double-sided substrate and the copper post that has been inserted through the penetrating hole are electrically conductive via the conductive adhesive. This configuration results in low long term reliability of the electrical connection against changes such as temperature or humidity caused by different thermal expansion coefficients among the electrically conductive adhesive and copper post as well as the conductor of the substrate. The low reliability is due to, for example, separation between the copper post and the electrically conductive resin or the occurrence of cracks in the electrically conductive resin. Also, due to the joining between different kinds of materials (that is, between a resin and a metal), the connection resistance is high and the heat conductivity is low.
A wiring substrate and a manufacturing method related to exemplary aspects of the present invention are described with reference to the figures. The same symbols are given to the same or equivalent portions in the drawings and the descriptions are not repeated. The size of each part in each drawing has been changed appropriately to facilitate understanding and may be different from the proportional ratio of the actual size.
As shown in
As shown in
The metal post 5 is column-shaped and the cross section thereof can be the same shape as the cross section of the internal space (through-hole conductor space) defined by the through-hole conductor 4. For example, if the cross section of (the internal space/through-hole conductor space defined by) the through-hole conductor 4 is circular in shape, the metal post 5 can also be cylindrically shaped and can also have a circular cross section. The metal post 5 and the through-hole conductor 4 are tightly fitted such that the metal post 5 and the through-hole conductor 4 are in face-to-face contact. Even if there is a partial gap between the metal post 5 and the through-hole conductor 4, the solder 6 can be inserted so as to fill in the gap.
As can be seen in the partially enlarged portion of
The metal post 5 and the through-hole conductor 4 come into face-to-face contact and, even if there is any gap, because the solder 6 can fill the gap, the connection resistance is small. As an example, in cases of in which both conductors include the same kind of metal as their main component, the resistance is extremely small. Furthermore, the metal post 5 and the through-hole conductor 4 are in face-to-face metal-against-metal contact, and hence the heat conductivity is high.
As shown in
Normally, the thermal expansion coefficients of the semiconductor chip 20 and the wiring substrate 10 are different, and even if the heat conductivity of the metal post 5 and the through-hole conductor 4 is high, the temperature gradient rises between the semiconductor chip 20 and the wiring substrate 10. Therefore, the resultant thermal expansion distortions of the semiconductor chip 20 and the wiring substrate 10 are different. Because the metal post 5 connecting the semiconductor chip 20 and the wiring substrate 10 is formed from a metal having a certain height, the metal post 5 changes its shape to absorb the difference in distortion so that the heat stress being applied to the semiconductor chip 20 and the wiring substrate 10 is mitigated.
As described above, regarding the wiring substrate 10 of the present embodiment, because the metal post 5 and the through-hole conductor 4 are tightly fitted and the metal post 5 and the through-hole conductor 4 are in face-to-face contact, the electrical resistance and the heat resistance in between these parts are small, thus allowing for a stable heat cycle, etc. As a result, the reliability of the electrical conductivity between the metal post 5 and the through-hole conductor 4 can be maintained for a long period of time. In addition, because a solder is applied to the end surface 5a of the metal post 5 that is in the through-hole conductor 4, the metal post 5 can be kept from being separated from the through-hole conductor 4.
Moreover, the end surfaces 5b of the metal posts 5 that project from the wiring substrate 10 can be on a single plane and the terminal of the semiconductor chip 20 can be subjected to soldering under the same conditions. As a result, the efficiency ratios of the electrical conductivity and the heat conductivity can be high. Furthermore, in this example, due to the connection between the metal post 5 and the through-hole conductor 4 being between identical materials, the connection resistance is lowered.
In one example aspect, the end surface 5b of the metal post 5 on the semiconductor chip 20 side of the wiring substrate 10 is parallel to the electrode surface of the semiconductor chip 20, and the end surface 5b of each metal post 5 of the wiring substrate 10 is on a single plane. In this example, the electrodes of the metal post 5 and the semiconductor chip 20 can more easily make metal to metal contact.
If the semiconductor chip 20 and the metal post 5 are connected using a solder, for example, the end surface 5b of each metal post 5 on the semiconductor chip 20 side does not have to be on a single plane with respect to the electrode surface of the semiconductor chip 20. This is because the solder can be filled in to realize electrical conductivity between the metal posts 5 and the electrode even if there is a distance gap between the metal post 5 and the electrode.
As noted above and as can be seen in
Next, a manufacturing method of the wiring substrate 10 having the above constitution is described with reference to the drawings. The manufacturing method described below is only an example, and the present invention is not limited to this example as long as the same results are obtainable.
Beginning with
A substrate 11 is depicted between the base material 8 and the die 60 in
As for the conductor 4 of the through-hole 3, the inner diameter (diameter of the internal space/through-hole opening or space defined by the conductor 4) thereof is formed with a tolerance so that the projection part 8a formed in the base material 8 is tightly fitted. As best illustrated in
As shown in
Instead of solder-joining the metal post 5 and the through-hole conductor 4, in another exemplary aspect, these two elements are joined by using an electrically conductive adhesive. In this example, the electrically conductive adhesive helps by filling in the gap between the metal post 5 and the through-hole conductor 4 in order to maintain the basic electrical conductivity between the metal post 5 and the through-hole conductor 4 through a face-to-face, metal-against-metal contact.
As illustrated in
In this example, the burr 5c at the peripheral rim of the end surface 5a of the metal post 5 cuts into the through-hole conductor 4 when the end surfaces 5b of the metal posts 5 that project from the substrate 11 are aligned (such as by the alignment step discussed above with reference to
If, for example, the material of the through-hole conductor 4 is softer than the material of the die 60 that is used for a punching process, the shoulder part of the through-hole conductor 4 is dragged onto the side of the metal post 5 and becomes smooth during the punching out (cutting) and pressing steps that are illustrated in
As for the wiring substrate related to the present invention, the metal post and the through-hole conductor are tightly fitted and the metal post and the conductor that is formed at the side wall of the through-hole are in face-to-face contact, and the electrical resistance and the thermal resistance in between are thus small and therefore stable against temperature changes. As a result, the reliability of the electrical conductivity of the wiring substrate and the heat cycle durability in heat conductivity are improved.
The embodiment disclosed herein is a non-restrictive example in every aspect. It is intended that the scope of the present invention include not only the above descriptions but also the equivalent meanings of the scope of the patent claims as well as all any changes made within the scope.
Obviously, numerous modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein.
Number | Date | Country | Kind |
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2007-230443 | Sep 2007 | JP | national |
The present application claims priority to Japanese Patent Application No. 2007-230443, filed Sep. 5, 2007 and U.S. Provisional Application No. 61/988,895, filed Nov. 19, 2007, the entire contents of each of which are hereby incorporated by reference.
Number | Date | Country | |
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60988895 | Nov 2007 | US |