US 20060076661 A1
Vias (210, 210B) are formed in a surface of a substrate. At least portions of contact pads (139, 350) are located in the vias. Contact pads (150, 340) of an integrated circuit structure are inserted into the vias and attached to the contact pads (139, 350) of the substrate. The vias provide a strong, reliable mechanical and electrical connection. A via may expose not only a contact pad (350) in the substrate but also a surrounding region. Solder (930) wets the contact pad better than the surrounding region, resulting in a stronger solder joint and better electrical conductivity. Alternatively, the contact may include multiple conductive layers (910.1, 910.2), with the top layer (910.2) being more solder wettable than the bottom layer (910.1) and the top layer covering only a portion of the bottom layer.
1. A structure comprising:
(1) a first integrated circuit structure comprising:
a semiconductor substrate;
one or more first conductive contact pads protruding out at a surface of the first integrated circuit structure;
(2) a first substrate comprising a circuit which comprises one or more first conductive contact pads, wherein at least a portion of each of the one or more first contact pads of the first substrate is located in a corresponding via in a surface of the first substrate;
wherein the protruding first contact pads of the first integrated circuit structure are inserted into the corresponding vias of the first substrate and attached to the first contact pads of the first substrate;
wherein each first contact pad of the first integrated circuit structure has a non-solder portion inside the corresponding via.
2. The structure of
3. The structure of
4. The structure of
5. The structure of
6. The structure of
7. The structure of
8. The structure of
9. The structure of
10. The structure of
11. The structure of
12. The structure of
13. The structure of
14. The structure of
15. The structure of
(4) a second integrated circuit structure comprising:
a semiconductor substrate;
one or more first conductive contact pads protruding out at a surface of the second integrated circuit structure;
wherein the first integrated circuit structure further comprises one or more second conductive contact pads, wherein at least a portion of each of the one or more second contact pads of the first integrated circuit structure is located in a corresponding via in a surface of the first integrated circuit structure;
wherein the protruding first contact pads of the second integrated circuit structure are inserted into the corresponding vias of the first integrated circuit structure and attached to the second contact pads of the first integrated circuit structure;
wherein each first contact pad of the second integrated circuit structure has a non-solder portion inside the corresponding via of the first integrated circuit structure.
16. The structure of
17. The structure of
18. The structure of
19. A first substrate comprising:
one or more conductive contact pads for attachment to circuitry; and
a dielectric having one or more openings over the one or more contact pads;
wherein a surface of at least one of the openings has a first portion which is a surface portion of one of the contact pads, and a second portion made from a different material than the first portion.
20. The first substrate of
21. The first substrate of
22. The first substrate of
23. The first substrate of
24. The combination of
25. The first substrate of
26. The first substrate of
The present application is a division of U.S. patent application Ser. No. 10/798,540 filed on Mar. 10, 2004 by S. Savastiouk et al., entitled “ATTACHMENT OF INTEGRATED CIRCUIT STRUCTURES AND OTHER SUBSTRATES TO SUBSTRATES WITH VIAS”, incorporated herein by reference, which is a continuation-in-part of U.S. patent application Ser. No. 10/739,788 filed on Dec. 17, 2003 by S. Savastiouk et al., entitled “INTEGRATED CIRCUITS AND PACKAGING SUBSTRATES WITH CAVITIES, AND ATTACHMENT METHODS INCLUDING INSERTION OF PROTRUDING CONTACT PADS INTO CAVITIES”, incorporated herein by reference.
The present invention relates to attachment of integrated circuits to other substrates.
Integrated circuit dies (“chips”) can be attached to a lead frame and then packaged in a ceramic or plastic carrier. The leads of the lead frame can then be soldered to a printed circuit board (PCB). Alternatively, the chip can be soldered directly to the PCB (“flip chip” packaging). The flip chip packaging reduces the package size and shortens the electrical connections between the die and the PCB.
In the manufacturing process, contact pad metal layer 137 (the layer that provides the contact pads) is deposited and patterned over the chip's silicon substrate 140. A passivation dielectric layer 147 is formed on layer 137. Openings are formed in dielectric 147 to expose the contact pads 137. As a result, contact pads 137 are recessed into the chip's surface. To connect the contact pads 137 to the PCB, protruding metal bumps 150 are formed on the contact pads. Bumps 150 are bonded to PCB contact pads 139 with solder, an adhesive, or by thermal or thermosonic compression.
Bumps 150 can themselves be made of solder. The chip is placed on the PCB with bumps 150 on pads 139, and solder 150 is reflowed to form solder joints. This attachment is mechanically strong and reliable in the presence of thermal stresses, but the solder bumps are difficult to scale down as contact pads 137 become smaller and the pitch between the pads 137 is reduced. As the solder bump sizes decrease to accommodate the smaller contact pads and pitches, the solder joints become mechanically and thermally weaker. Also, the solder ball (solder bump) size defines the standoff distance between the chip 124 and PCB 130. If the standoff is too small, there will be increased fatigue stresses on the solder joints during thermal cycling. In addition, there is a greater possibility of undesirable residues remaining between the chip 124 and the PCB and causing some degradation.
Bumps 150 can also be made without solder, e.g. from copper (Cu) or gold (Au), to obtain better scalability. See S. Zama et al., “Flip Chip Interconnect Systems Using Wire Stud Bumps and Lead Free Solder”, 2000 Electronic Components and Technology Conference, pages 1111-1117 (available from IEEE); C. H. Wang et al., “Laser-Assisted Bump Transfer for Flip Chip Assembly”, 2000 International Symposium on Electronic Materials & Packaging, pages 86-90 (available from IEEE), both incorporated herein by reference. A combination of solder and copper has also been used. More particularly, a “copper pillar” can be plated on contact pads 137, then solder is plated on the copper pillar. See H. Lu et al., “Predicting Optimal Process Conditions for Flip-Chip Assembly Using Copper Column Bumped Dies”, 2002 Electronics Packaging Technology Conference, pages 338-343 (available from IEEE); Tie Wang et al., “Studies on a Novel Flip-Chip Interconnect Structure—Pillar Bump”, 2001 Electronic Components and Technology Conference (available from IEEE), both incorporated herein by reference.
Improved integrated circuit attachment techniques are desirable.
This section summarizes some features of the invention. Other features are described in the subsequent sections. The invention is defined by the appended claims which are incorporated into this section by reference.
In some embodiments of the present invention, cavities are formed in the PCB, and the integrated circuit bumps are inserted into the cavities. For example, in
In some embodiments, cavities 210 increase the mechanical strength of the structure. The structure becomes stronger against lateral forces (including lateral stresses caused by thermal expansion). Also, the amount of solder or adhesive can be increased by increasing the depth of cavities 210 without increasing the lateral size of the structure. Improved scalability is therefore provided.
In addition, if bumps 150 are attached with solder or a conductive or anisotropic adhesive, the size uniformity requirements for bumps 150 are relaxed. If the bumps are not uniform in size, the shorter bumps will still provide a reliable electrical connection to contacts 139 as long as there is a reliable electrical connection between the bumps and the solder or adhesive in cavities 210.
Bumps 150 can be thought of as “contact pads”, and the invention is applicable to any protruding contact pads and not necessarily the protruding pads formed by bumping a die. For example, protruding contact pads can be formed on a die by removing the die material to expose metal features, as described in U.S. Pat. No. 6,322,903 issued Nov. 27, 2001 to Siniaguine et al. and incorporated herein by reference.
In some embodiments, layer 220 is absent, and a cavity 210 exposes not only the contact pad 139 but also a surrounding dielectric region in substrate 130. The solder (not shown) wets the contact pad 139 better than the surrounding region, so more solder gathers near the bump 150, and the solder reaches up higher along the surface of bump 150. This is believed to provide a stronger solder joint and better electrical conductivity at least in some embodiments. Alternatively, the contact pad 139 or layer 220 may include multiple conductive layers, with the top layer being more solder wettable than the bottom layers and the top layer covering only a portion of the bottom layers. The solder will preferentially wet the more solder wettable layer, gathering closer to bump 150 and reaching up higher.
The invention is not limited to the embodiments discussed in this section. For example, cavities 210 can be replaced by through vias (through holes) that pass through the PCB 130. Contacts 139 can be metal layers on the sidewalls of the through vias. The integrated circuit structure 124 can be a wafer rather than a die. PCB 130 can be replaced with a ball grid array substrate (BGA) or some other packaging substrate, e.g. a silicon interposer. PCB 130 can also be replaced with another integrated circuit structure (a die or a wafer). Other features and advantages of the invention are described below. The invention is defined by the appended claims.
The embodiments described in this section illustrate but do not limit the invention. The invention is not limited to particular materials, process steps, or dimensions. The invention is defined by the appended claims.
Dies 124 are attached to interposer 120 as in
Silicon interposer 120 includes metal layers 136 formed over silicon substrate 140. Substrate 140 has substantially planar top and bottom surfaces, and is quite thin. In some embodiments, the planarity of substrate 140 is suitable for fine geometry photolithography (finer than possible with BT and FR4 substrates). The thickness of substrate 140 can be 100 μm or less (50 μm to 35 μm thickness values believed to be achievable, and smaller values may be possible). Layers 136 provide interconnect lines and may also provide power and ground planes, resistors, inductors, capacitor plates for decoupling capacitors and other capacitor types, and possibly other elements, known or to be invented. Layers 136 can be separated from each other, and from the substrate, by dielectric layers 144. Layers 136 contact each other and the silicon substrate through openings in the dielectric layers. Layers 136 can also be formed directly on the silicon substrate if desired. Layers 136 provide contact pads 136C at the top surface of the interposer. At least a portion of each contact pad 136C is located in a corresponding cavity 210.
These features are exemplary and not necessary. For example, silicon substrate 140 can be thicker than described above, and its top and bottom surfaces do not have to be planar.
In the embodiment of
Interconnects (not shown) in BT substrate 110 connect the contact pads 350 to contact pads 360 at the bottom surface of substrate 110. Solder balls 134 are formed on pads 360 by conventional techniques for attachment to PCB 130.
The size and spacing (pitch) of contact pads 136C on interposer 120 matches the size and the pitch of the contact pads on dies 124. If dies 124 are silicon integrated circuits, their CTE (coefficient of thermal expansion) matches the CTE of the interposer, so the pitch of contact pads 136C can be small because the low thermal stresses at the interface between the dies and the interposer make it unnecessary to use large bumps 150 as would be desirable for a strong mechanical connection. The contact pads 340 on the bottom of the interposer match the top contact pads 350 of BT substrate 110. For some fabrication technologies, the minimum dimensions are as shown in the following Table 1. The dimensions can typically be reduced if more expensive technologies are used.
Silicon interposer 120 can be manufactured using conventional techniques. See e.g. the aforementioned U.S. Pat. No. 6,322,903. Other techniques are described in U.S. patent application Ser. No. 10/410,929 filed on Apr. 9, 2003 by P. Halahan et al., entitled “Electroplating and electroless plating of conductive materials into openings, and structures obtained thereby”, incorporated herein by reference. Still other techniques can possibly be used, whether known or to be invented. An exemplary manufacturing process is as follows. Vias 330 (
Optionally, gold (Au) layer 444 and nickel (Ni) layer 448 are electroplated, in that order, to an exemplary thickness of 0.2 μm and 1.0 μm respectively.
Copper 430.2 is electroplated on nickel 448 to fill the vias 330 and possibly protrude out of the vias. In the electroplating of layers 444, 448, 430.2, the cathode terminal (not shown) of the power source is placed at the periphery of wafer 140 in physical contact with seed layer 430.1.
Optionally, nickel (Ni) layer 450 is electroplated on the top surface of copper layer 430.2 to an exemplary thickness of 0.5 μm.
Resist 440 is removed (
Then a CMP step (chemical mechanical polishing) is performed to remove copper 430.2, nickel 448, gold 444, and TiW 420 off the top surface of substrate 140 (
In an alternative embodiment, the wet etch of copper 430.1 is omitted, and copper 430.1 is removed by the CMP step. The separate wet etch of copper 430.1 may be desirable however because it may shorten the more expensive CMP step, thus reducing the total manufacturing cost.
Oxide 410 can be patterned if desired. Metal layers 136 (
Solder balls 720 are formed on contact pads 136C, by any suitable technique. For example, solder paste can be deposited to cover the interposer wafer 120, and then wiped off by a squeegee blade to force the solder into cavities 210 and remove it from the top surface of the top layer 144. In some embodiments, interconnects 136 are made of copper, and contact pads 136C are plated with a layer 710 of nickel or gold. Layer 710 does not dissolve in solder 720 and provides a barrier for the copper diffusion from interconnects 136, so the melting temperature of solder 720 does not change when the solder is reflowed.
In some embodiments, the solder is not placed at this stage to avoid solder melting at high temperatures present in plasma wafer thinning processes described below in connection with
Then the interposer wafer is thinned from the bottom to expose the gold 444. See
The plasma etch forms copper oxide (not shown) on the exposed portions of copper 430.1. The copper oxide and the copper 430.1 are etched by a wet etch to expose gold 444. The gold provides a solderable oxide-free surface. Nickel 448 will prevent copper diffusion from layer 430.2 into the solder. The copper diffusion may be undesirable because it increases the solder melting temperature. In other embodiments, the copper diffusion is desirable to achieve a certain solder hierarchy (the hierarchy of the melting temperatures of different solders) as explained below. In such embodiments, the etch of copper 430.1 can be omitted. Nickel 448 can also be omitted.
As stated above, gold 444 can be omitted. The etch of copper 430.1 will then expose nickel 448.
In some embodiments, the copper 430.1 is not etched away. The copper oxide (not shown) on copper 430.1 can be removed by a wet etch. The copper oxide can also be removed by a solder flux during soldering of the interposer wafer to BT substrate 110 (the soldering operation is described below). Layers 444, 448 can be omitted.
Metal contact pads 340 are metal protrusions formed by the metal layers 430.2, 448, 444, 430.1, 420 below the bottom surface of silicon 140. In some embodiments, the height Hd of metal contact pads 340 is 50 μm.
A dielectric layer (not shown) can optionally be formed on the bottom surface or the interposer to cover the silicon 140 but not the metal contact pads 340. The dielectric can be formed without photolithography. See the aforementioned U.S. Pat. Nos. 6,322,903 and 6,498,381 and U.S. patent application Ser. No. 10/410,929.
The interposer wafer can be diced if desired. The dicing can be performed at the same time as the interposer wafer thinning if vias were formed along the dicing lines (scribe lines) simultaneously with vias 330 at the stage of
In some embodiments, the interposer wafer is not diced. ICs 124 will be attached to the undiced interposer wafer.
In some embodiments, metal 430.2 does not fill the through-silicon vias. Metal 430.2 is a thin film deposited over the via sidewalls, and it can be part of a layer 136. See the aforementioned U.S. Pat. No. 6,498,381. Also, in some embodiments the contact pads 340 do not protrude out of the bottom surface of the interposer.
BT substrate 110 (
Top contact pads 350, and the top metal layer 910, are formed below the top BT layer 110.3. In
In one embodiment, each BT substrate cavity 210B has a diameter Dcav=150 μm to accommodate a 50 μm to 60 μm diameter Dc of the contact pads 340. Dc can be calculated starting with the diameter Dv (
Cavities 210B are filled with solder paste 930. In one embodiment, the solder paste is deposited to cover the BT substrate, and then is wiped off by a squeegee blade to force the solder into cavities 210B and remove it from the top surface of BT layer 110.3. The solder is chosen to have a high melting temperature to provide a desired solder hierarchy for subsequent solder attachment of dies 124 and PCB 130. In some embodiments, the solder paste is a no-clean type NC253 available from AIM of Montreal, Canada. This paste incorporates solder flux but there is no need to clean the flux after the solder reflow.
No-flow underfill 940 (dielectric) is dispensed on BT substrate 110 at the future site of interposer 120. In some embodiments, the underfill is type STAYCHIP™ 2078E available from Cookson Electronics, a company having an office in Georgia, the United States of America. This underfill performs both the underfill function and the solder flux function. The underfill can be dispensed with a dispensing system of type CAMELOT/SPEEDLINE 1818 available from Cookson Electronics.
Interposer wafer 120 is placed on BT substrate 110 (
Underfill 940 spreads out under the interposer. In the embodiment shown, the bottom surface of silicon 140 does not reach the BT substrate. Underfill 940 helps insulate the silicon from solder 930. Therefore, it is unnecessary to form a dielectric layer on the bottom silicon surface.
The interposer placement can be performed with a placement tool of type SIPLACE F4 available from Siemens corporation of Germany. The placement tool picks up the interposer from the top by a vacuum holder 1010 schematically shown in
The structure is heated to reflow the solder paste 930 and cure the underfill 940. The solder wets the bottom and side surfaces of copper contact pads 340. In one embodiment, the final value of the gap G1 between the silicon 140 and the BT substrate 110 is 25 μm. The gap values of 5 to 10 μm and larger are believed to be appropriate to provide sufficient electrical insulation if no dielectric is formed on the bottom surface of silicon 140. The contact 340 portion inside the vias 210B is 25 μm high (C1=25 μm in
If the solder 720 was placed on the interposer before the interposer attachment to BT substrate 110, solder 720 may or may not be reflowed during this step depending on the solder 720 melting temperature.
Then vacuum holder 1010 releases the interposer.
In some embodiments, the vacuum holder releases the interposer before the reflow of solder paste 930. The interposer stays in place due to a surface tension between silicon 140 and the underfill 940. Multiple interposers can be placed on BT substrate 110, and the solder reflow and underfill curing can be performed in a single heating step for all the interposers, after the vacuum holder 1010 is removed. A similar technique has previously been applied for flip-chip mounting of dies on a BT substrate, as described in M. Painaik and J. Hurtley, “Process Recommendations for Assembly of Flip Chips using No-flow Underfill”, Technical Bulletin, Cookson Semiconductor.
In the BT embodiment described above, the BT layers 110.1, 110.2, 110.3 are laminated on top of each other. Each layer 110.1, 110.2 is a solid sheet placed on the structure in a solid form. In some embodiments, the top layer 110.3 is made from a material different from the material of layers 110.1, 110.2. For example, solder dam materials can be used, such as photoimageable polyimide, Dupont VACREL 8100, Dupont Flexible Photolmageable Coverlay (PIC) 1000 & 2000, Shipley (Dynachem) DynaMASK 5000, Shipley ConforMASK 2500, and possibly others. Some of the solder dam materials (e.g. polyimide) can be deposited in a liquid (possibly viscous) form and then cured.
In some embodiments, solder 720 has a lower melting temperature than solder 930. Therefore, solder 930 is not melted during the attachment of dies 124.
In other embodiments, solder 720 initially has the same or higher melting temperature than solder 930, but the melting temperature of solder 930 is increased during the attachment of interposer 120 to BT substrate 110. The melting temperature of solder 930 becomes higher than the melting temperature of solder 720. The melting temperature of solder 930 is increased because the copper from layer 220 and/or layer 350 dissolves in solder 930. In the embodiment of
Metal contact pads 136C can be formed from a material other than copper. This may be desirable if solder 720 is placed on the interposer before the interposer attachment to BT substrate 110, because copper in pads 136C could diffuse in solder 720 during the interposer attachment to the BT substrate and increase the solder 720 melting temperature. In some embodiments, interconnects 136 are made of copper, but contact pads 136C are plated with a layer 710 of nickel or gold. Layer 710 does not dissolve in solder 720 and provides a barrier for the copper diffusion from interconnects 136, so the melting temperature of solder 720 does not change. In other embodiments, the melting temperature of solder 720 changes during the attachment of the interposer to substrate 110, but the melting temperature of solder 720 remains below the melting temperature of solder 930.
Each die 124.1 has one or more metalized through vias 330.1 formed in the die's semiconductor substrate 140.1 (e.g. monocrystalline silicon). Each via 330.1 passes between the top and bottom surfaces of substrate 140.1. Conductive paths are provided from contact pads at the top of each die 124.1 to contact pads 340.1 at the bottom of the die through the vias 330.1. Contact pads 340.1 protrude out of the respective vias 330.1. The dies 124.1 can be manufactured using the same techniques as described above for interposer 120 (involving the wafer thinning to expose the contact pads 340.1). Each die may have the same general structure as interposer 120 in
In some embodiments, dies 124.1 and interposer 120 have devices (e.g. transistors, diodes, and others) manufactured at the top surface (active surface). Transistor source/drain regions, diodes' cathodes and anodes, and other elements can be formed in semiconductor substrates 140.0, 140.1 of interposer 120 and dies 124.1 at the top surface of the respective substrates. Cavities 210.1 are formed in the top surface of dies 124.1, and solder balls 720.1 are formed in the cavities on the dies' top contact pads, possibly before the wafer thinning operation exposing the contact pads 340.1, as in
Dies 124.2 may be similar to dies 124.1. Dies 124.2 include metalized vias 330.2 in semiconductor substrates 140.2, and contact pads 340.2 protruding out of the vias on the bottom. Dies 124.2 may contain devices (e.g. transistors, diodes, and others) manufactured at the top surface (active surface) of semiconductor substrates 140.2. Transistor source/drain regions and other elements can be formed in semiconductor substrates 140.2 at the top surface. Cavities 210.2 are formed in the top surface of dies 124.2, and solder balls 720.2 are formed in the cavities on the dies' top contact pads, possibly before the wafer thinning operation exposing the contact pads 340.2, as in
The third level dies 124.3 are like dies 124 in
The manufacturing sequence is shown in
In some embodiments, all of solders 720.0, 720.1, 720.2, 930 are initially the same material. In an illustrative example, the solders are eutectic type LF 128 described above, with the initial melting temperature of 218° C. The melting temperature of solder 930 increases to about 230° C. in step 1420.
At step 1430, dies 124.1 are soldered to interposer 120 with solder 720.0, at a temperature of about 218° C. or higher, but below 230° C. not to melt the solder 930. Contact pads 340.1 are inserted into cavities 210.0 of interposer 120. The copper from contact pads 340.1 dissolves in solder 720.0 and increases its melting temperature to about 230° C. Solder 720.1 may be placed on dies 124.1 in advance and may melt, but its melting temperature does not increase because the solder 720.1 is not in contact with copper or other material that could increase the solder melting temperature (the top surface portions of the top contact pads of die 124.1 are made of suitable materials to ensure that the solder melting temperature does not increase).
At step 1440, dies 124.2 are attached to dies 124.1 with solder 720.1, at a temperature below 230° C. Contact pads 340.2 are inserted into cavities 210.1 of dies 124.1. Solders 720.0 and 930 do not melt. The melting temperature of solder 720.1 is increased to about 230° C. due to the diffusion of copper from contact pads 340.2.
At step 1450, dies 124.3 are flip-chip attached to dies 124.2 with solder 720.2, at a temperature below 230° C. Bumps 150 are inserted into cavities 210.2 of dies 124.2. Solders 930, 720.0, 720.1 do not melt. If desired, bumps 150 may include copper to increase the melting temperature of solder 720.2. The higher melting temperature may be desirable to prevent the solder melting during the attachment of BT substrate 110 to PCB 130 (
Many variations are possible. For example, any number of dies can be used at each level. Also, one or more dies 124.2 can be attached directly to interposer 120, i.e. there may be three levels of dies over one interposer area but only two levels of dies over another interposer area. Any number of die levels can be present in different interposer areas. Dies 124.3 may be omitted. Dies 124.2 may have no contact pads on the top, or they may have contact pads on the top which can be wire bonded to other substrates.
Other solder types and melting temperatures can be used, and materials other than copper can be used to increase the melting temperatures. Different materials and contact pad structures can be used in different dies. Different semiconductor substrates can be different semiconductor materials in the same structure.
Varying the solder melting temperature to achieve a desired solder hierarchy is not limited to the interposer structures, but may be used in other semiconductor packages, known or to be invented, with or without interposers.
The invention is not limited to any particular manufacturing sequence however.
In some embodiments, the same dimensions are obtained for the attachment of dies 124.1, 124.2, 124.3 as for the attachment between the BT substrate and the interposer. More particularly, the final value of the gap between the silicon 140.1 and interposer 120 or between the silicon 140.2 and the dies 124.1 is 25 μm (gap values of 5 to 10 μm and larger are believed to be appropriate to provide sufficient electrical insulation if no dielectric is formed on the bottom surface of silicon 140.1 or 140.2); the portions of contacts 340.1, 340.2, 150 inside the respective cavities 210.0, 210.1, 210.2 are 25 μm high (note dimension C1 in
Underfill (not shown) can be injected between the interposer and the dies 124.1, between the dies 124.1 and 124.2, and between the dies 124.2 and 124.3 using known techniques. No flow underfill can also be used.
The advantage of the contact pad 350 as in
Assuming the solder paste filled the cavity before the solder reflow, and ignoring the thickness of pad 350, the solder paste volume Vc was the cavity volume, i.e.:
We will assume that the solder paste was half solder and half flux. After the reflow, the solder volume Vs is therefore one half of Vc, i.e.
Also, Vs is the volume of the truncated solder sphere, and therefore:
From (2) and (3) we obtain:
Example: suppose Dc=150 μm, Hc=50 μm, Db=80 μm. From equation (4):
From equation (5):
From equation (6):
Other examples are given in the following Table 2 for Dc=150 μm. The dimensions are in micrometers. Tilda (“˜”) denotes approximation.
The invention is not limited to the embodiments described above. For example, non-eutectic solders can be used. The “melting temperature” is any temperature as high or higher than the solidus and but not higher than the liquidus. As is known, the solidus is the highest temperature at which 100% of the solder is solid, i.e. the solder is just beginning to melt. The liquidus is the lowest temperature at which 100% of the solder is liquid. For a eutectic solder, the solidus and the liquidus are the same.
Also, in some embodiments, the cavities 210B (
The interposer may include capacitors having a capacitance of 5.0 pF or higher. For example, capacitance values of 10 pF, 100 pF, or higher have been used on circuit boards to decouple the power lines from the ground lines or for other purposes, and such capacitors can be manufactured in the interposer. Resistors having resistance values of 10 Ω and higher (e.g. 50 Ω, 100 Ω, or 150 Ω) are used on circuit boards for line termination and other purposes, and they can be manufactured in the interposer. Inductors having inductance values of 100 nH or higher are commonly used on circuit boards and can be manufactured in the interposer. The invention is not limited to particular capacitance, resistance or inductance values. Other embodiments and variations are within the scope of the invention, as defined by the appended claims.