SOLDERLESS AND PRESSURE CONTACT CONNECTION

A pressure contact assembly includes a power substrate, a chip, and a lead. The power substrate has a surface connected to a ceramic tile and a cavity. The chip is soldered to the surface. The lead is to be inserted into the cavity and has a top portion to connect to an external device and a bottom portion to fit into the cavity.

FIELD OF THE DISCLOSURE

Embodiments of the present disclosure relate to direct copper bonded (DCB) and active metal brazed (AMB) substrates and, more particularly, to soldering issues for these substrates.

BACKGROUND

Substrates for power electronics are different than printed circuit boards used for low power microelectronics. The power electronics substrate both provides the interconnections to form an electrical circuit and cool the components. Power electronic substrates carry higher currents and provide a higher voltage isolation (up to several thousand volts), as compared to microelectronic counterparts, and operate over a wide temperature range (e.g., up to 200° C.).

Direct bonded copper (DBC), also known as direct copper bonded (DCB) substrates, have very good thermal conductivity, and are thus suitable for power modules. DCBs are composed of a ceramic tile with a sheet of copper bonded to one or both sides of the ceramic tile. Suitable for smaller lots, active metal brazed (AMB) substrates involve the attachment of thick metal layers to ceramic plates. Insulated metal substrates (IMS) are also used for power modules and consist of a metal baseplate covered by a thin layer of dielectric and a layer of copper. IMS are single-sided substrates.

When bonding a power electronics substrate to a power lead, there may exist system reliability issues with the soldering. A phenomenon known as “cold solder” can compromise the bond between the power lead and the substrate over time, particularly when the power electronics substrate is operating in a harsh environment.

It is with respect to these and other considerations that the present improvements may be useful.

SUMMARY

An exemplary embodiment of a pressure contact assembly in accordance with the present disclosure may include a power substrate, a chip, and a lead. The power substrate has a surface connected to a ceramic tile and a cavity. The chip is soldered to the surface. The lead is to be inserted into the cavity and has a top portion to connect to an external device and a bottom portion to fit into the cavity.

Another exemplary embodiment of a pressure contact assembly in accordance with the present disclosure may include a lead and a power substrate. The lead has a first portion and a second portion connected to the first portion. The first portion connects to an external device. The second portion is perpendicular to the first portion and has a modification to its smooth surface. The power substrate has a first surface connected to a ceramic tile. The first surface has a cavity inside which the modification is press-fit.

DETAILED DESCRIPTION

Several embodiments of pressure contact assemblies are disclosed herein. The pressure contact assemblies each feature a power substrate having a ceramic tile sandwiched between two DCB or AMB surfaces or a power substrate having a ceramic tile disposed atop an insulated metal substrate. The power substrate has one or more cavities etched out of the top surface and may feature both over-etches and under-etches, where the under-etches may be half-etches, in some embodiments. The power lead (terminal) is adapted to have a top portion that is much like prior art leads, whereas the bottom portion is modified to be fit into the one or more cavities in a variety of ways. Modifications are made to the ceramic tile to improve the ability of the power substrates to support pressure contact assembly.

For the sake of convenience and clarity, terms such as “top”, “bottom”, “upper”, “lower”, “vertical”, “horizontal”, “lateral”, “transverse”, “radial”, “inner”, “outer”, “left”, and “right” may be used herein to describe the relative placement and orientation of the features and components, each with respect to the geometry and orientation of other features and components appearing in the perspective, exploded perspective, and cross-sectional views provided herein. Said terminology is not intended to be limiting and includes the words specifically mentioned, derivatives therein, and words of similar import.

As used herein, power substrates refer variously to direct bonded copper (DBC), also known as direct copper bonded (DCB) substrates, active metal brazed (AMB) substrates, and insulated metal substrates (IMS). The principles shown and described herein may refer to any of these types of substrates. For simplicity, these substrates are referred to as power substrates.

FIGS.1A-1Bare representative drawings of a cold solder problem experienced with power substrates, according to the prior art.FIG.1Ashows a lead (terminal)102partially surrounded by solder106, where the solder106attaches the lead to a pad104of a power substrate.FIG.1Bis a close-up view of the lead102, solder106, and pad104. In both illustrations, cracks have formed in the solder106, a phenomenon known as cold solder. Cold solder occurs when the solder cracks, which may occur over time, and is more likely to occur in harsh environments. If the cracks become large enough, the lead102is no longer able to form an electrical connection with the pad104. Thus, the solder106is no longer functioning as intended, causing the electronic circuit to become unreliable.

FIG.2is a representative drawing of a press-fit solution used to replace soldering in printed circuit boards (PCBs), according to the prior art. A lead (terminal)202is shaped to fit securely into an aperture206of a PCB204. The lead202is slender at one end, the end to be inserted into the aperture206, but more bulbous at a center portion, where the diameter of the more bulbous portion is slightly larger than the diameter of the aperture206. Once the lead202is press-fit into the aperture206of the PCB204, the bulbous portion partially compresses in the aperture, forming a tight fit in the PCB204. A top view208and a side view210are also shown.

Though there are variations, PCBs are typically made using a material known as FR4 (fire-retardant 4), which is a composite material consisting of woven fiberglass cloth combined with an epoxy resin binder. PCBs thus have some flexibility, which makes them suitable for press-fitting leads through their structure. Power substrates, on the other hand, are made using metal and ceramic, which are less flexible materials. Adding via holes in a power substrate is doable and the press fit pin can be inserted into the via holes. However, the components on the power substrate will lose the electrical isolation that characterizes power substrates, thus defeating the purpose of using power substrates. The traditional press-fitting illustrated inFIG.2is thus not suitable for power substrates.

FIGS.3A-3Bare representative drawings showing soldering on power substrates, according to the prior art.FIG.3Ais a perspective view andFIG.3Bis a side view of a power substrate314. The power substrate314consists of a first surface308and a second surface312, with a ceramic tile310sandwiched therebetween. The power substrate314may thus be a DCB substrate, with the first surface308and second surface312being direct copper bonded material. Or the power substrate314may be an AMB substrate, with the first surface308and the second surface312being active metal brazed material. Disposed on the power substrate314is a power chip302(hereinafter, “chip302”) and a power lead (terminal)304(hereinafter, “lead304”), which are attached to the power substrate314using solder. Solder306aand306bare used to attach the chip302to the power substrate314while solder306cand306dare used to attach the lead304to the power substrate314(collectively, “solder306”). The solders306a-dmay be regular solders, high-lead solders, lead-free solders, such as Ag-sintered, and so on. Or the solder306aand306bmay be one type of solder while the solder306cand306dis a second type. Where the solders306are the same, the chip302and the lead304may be advantageously attached to the power substrate314in one process.

The solders306cand306dused to attach the lead304to the power substrate314may experience cold solder over time and in the presence of unfavorable environmental conditions. Where there is generally minimal thermo-mechanical stress on the chip302, there may be significantly more thermo-mechanical stress on the lead304, partly because the lead304is connected to an external circuit which might induce mechanical stress. Further, because both ends of the lead304are fixed, one side to the power substrate314and the other side to the external circuit, the lead304may experience higher thermo-mechanical stress during expansion and contraction which may occur over time. Thus, solder306aand306bon the chip302typically does not get stressed as much as solder306cand306don the lead304. The result may be an unreliable connection between the lead304and the power substrate314. Since the lead304is connected to an external device, such as a busbar, other terminal, or PCB, the failure of the solders306cor306dwill isolate the chip302from the rest of the circuitry and prevent it from functioning.

FIGS.4A-4Dare representative drawings of a pressure contact assembly400, according to exemplary embodiments.FIG.4Ais a perspective view,FIG.4Bis a side view, andFIGS.4C-4Dare detailed side views of two different embodiments of the pressure contact assembly400. The power substrate414consists of a first surface408and a second surface412, with a ceramic tile410sandwiched therebetween. The power substrate414may thus be a DCB or an AMB substrate. In a non-limiting example, the pressure contact assembly400may alternatively be a single-sided power substrate414, such as IMS. Disposed on the power substrate414is a power chip402(hereinafter, “chip402”) and a power lead (terminal)404(hereinafter, “lead404”), which are attached to the power substrate414using solder406. Alternatively, the chip402may be attached to the power substrate414using Ag sintering.

The pressure contact assembly400utilizes 1) a cavity422formed in the power substrate414; 2) a modification to the lead404to fit into the cavity422; and optionally, 3) a modification to the ceramic tile410to facilitate successful connection between the lead404and the power substrate414. The cavity422may be formed in a variety of ways known to those of skill in the art. In exemplary embodiments, the cavity422is formed by etching or otherwise cutting away the first surface408of the power substrate414, exposing the ceramic tile410at the cavity422. Alternatively, the first surface408may be partially etched away such that the ceramic tile410is not exposed at the cavity422. In either case, the cavity422has sufficient depth to accommodate the base of the lead404, as described further below.

In exemplary embodiments, the lead404consists of a top portion416and a bottom portion420in which the top portion416is split into two opposing sections. The bottom portion420further includes a pressure portion418.FIGS.4C-4Dillustrate alternative pressure contact assemblies400A and400B, respectively (collectively, “pressure contact assembly400” or “pressure contact assemblies400”). Lead404aconsists of top portion416aand bottom portions420aand420b, which include pressure portions418aand418b, respectively; lead404bconsists of top portion416band bottom portions420cand420d, which include pressure portions418cand418d, respectively (collectively, “top portion(s)416”, “pressure portion(s)418”, and “bottom portion(s)420”). The top portion416looks like the top of lead304. Thus, connecting the lead404to external circuitry is not impacted by the design change over the prior art.

The bottom portions420are curved like ribbon candy (with multiple waves) and are oppositional to one another (like mirror image S structures). Looking at the pressure contact assembly400A (FIG.4C), for example, bottom portion420aextends downward from top portion416a, curves to the left, curves to the right, then curves again to the left until being disposed horizontally (perpendicular to top portion416a); bottom portion420balso extends downward from top portion416a, curves to the right, curves to the left, then curves again to the right until being disposed horizontally (perpendicular to top portion416a). In exemplary embodiments, the top portion416is split into two different bottom portions420aand420b, with bottom portion420ahaving two distinct parts,420a1and420a2, as illustrated inFIG.4A, where bottom portion420boccupies the center of the lead404, and bottom portions420a1and420a2are disposed on either side of bottom portion420b. InFIGS.4B-4D, bottom portion420a2is not visible, being “behind” the other bottom portions420a1and420b. Thus, for both the pressure contact assemblies400A and400B, the top portion416of the lead404is split into a first s-shaped section416a1/416c1, a second s-shaped section416b, and a third s-shaped section416a2/416c2, where the second s-shaped section416bis disposed between the first s-shaped section416a1/416c1and the third s-shaped section416a2/416c2, and the second s-shaped section416bis a mirror image of the first s-shaped section416a1/416c1and the third s-shaped section416a2/416c2.

The result of this design is a lead404athat has movement in the form of spring action. In exemplary embodiments, by pushing the bottom portions420aand420btoward one another at pressure portions418aand418b, respectively, this causes bottom portions420aand420bto move toward one another. The lead404athus has a resting state (bottom ofFIG.4C) and a compressed state (top ofFIG.4C). Bottom portion420acan move a width, w1, in a leftward direction while bottom portion420bis able to move a width, w2, in a rightward direction, where widths w1and w2may be equal (w1=w2) or not equal (w1≠w2). Cavity422has a width, w3. In the resting state of lead404a, the distal ends of bottom portions420aand420bare a width, w3, apart while, in the compressed state of lead404a, bottom portions420aand420bare a width, w3−(w1+w2) apart.

To attach the lead404ato the power substrate414, the pressure portions418aand418bare pressed toward one another, causing the lead404ato be in its compressed state. The lead404is then moved downward toward the cavity422until the bottom portions420aand420btouch the bottom of the cavity422. The pressure portions418aand418bare then released so that they spring back until the lead404is in its resting state. In exemplary embodiments, horizontal pressure is applied to the pressure portions418aand418bto make a solderless contact between bottom portions420aand420band to the wall of cavity422, ensuring a tight coupling therebetween without need of solder. The lead404is thus fastened to the power substrate414.

The pressure contact assembly400B (FIG.4D) is slightly different than the pressure contact assembly400A. Bottom portion420cextends downward from top portion416band curves to the right, then curves slightly to the left, extends vertically downward, then curves to the left in a horizontal disposition; bottom portion420dalso extends downward from top portion416band curves to the left, then curves slightly to the right, extends vertically downward, then curves to the right in a horizontal disposition. In exemplary embodiments, the top portion416bis split into bottom portions420cand420d, with bottom portion420chaving two distinct parts,420c1and420c2, as illustrated inFIG.4A, where bottom portions420c1and420c2are disposed on either side of bottom portion420b. InFIGS.4B-4D, bottom portion420c2is not visible, being “behind” the other bottom portions420c1and420b. The base of bottom portions420cand420dare thus orthogonal to the top portion416b.

Like lead404a, lead404bhas movement in the form of spring action. In exemplary embodiments, by pushing the pressure portions418cand418dtoward one another, this causes bottom portions420cand420dto move away from one another. The lead404bthus has a resting state (top ofFIG.4D) and an expanded state (bottom ofFIG.4D). Bottom portion420ccan move a width, w4, in a leftward direction while bottom portion420dis able to move a width, w5, in a rightward direction, where widths w4and w5may be equal (w4=w5) or not equal (w4≠w5). Cavity422has a width, w6. In the resting state of lead404b, the distal ends of bottom portions420cand420dare a width, w6−(w4+w5) apart while, in the expanded state of lead404b, bottom portions420cand420dare a width, w6apart.

To attach the lead404bto the power substrate414, the lead404bis first moved downward until the bottom portions420cand420dare inside the cavity422. Pressure portions418cand418dare pressed toward one another, causing the bottom portions420cand420dto move and remain apart (the expanded state). In exemplary embodiments, horizontal pressure is applied to the pressure portions418cand418dto make a solderless contact between bottom portions420cand420dand to the wall of the cavity422, ensuring a tight coupling therebetween without need of solder.

FIGS.5A-5Bare representative drawings of pressure contact assemblies500A and500B, according to exemplary embodiments.FIG.5Apresents side views of pressure contact assembly500A whileFIG.5Bpresents side views of pressure contact assembly500B. Pressure contact assembly500A is the pressure contact assembly400A, modified to include resistance welding; pressure contact assembly500B is the pressure contact assembly400B, modified to include resistance welding (collectively, “pressure contact assembly500” or “pressure contact assemblies500”). Join terminals502aand502bare shown inFIG.5Awhile join terminals502cand502dare shown inFIG.5B(collectively, “join terminal(s)502”). In exemplary embodiments, resistance welding is performed at the join terminals502, causing the bottom portions420of the respective leads404to soften/melt. Resistance welding is the joining of metals by applying pressure and passing current through the metal area to be joined. No additional materials such as solder, are needed to melt the bottom portions420against the first surface408of the power substrate414. Resistance welding is done at high current (typically, greater than 110 A) with lower voltage (typically, 4-12 V) in which the two-input terminal either (+) or (−) can be at any position.

The following pressure contact assemblies are characterized as having L-shaped power leads (terminals) in which the top portion is for connection to an external device. The bottom portion, which is perpendicular to the top portion, includes one or more modifications from being an otherwise smooth surface. The one or more modified portions of the lead are press-fit into the power substrate. The surfaces of each power substrate have likewise been over-etched, under-etched, and/or half-etched to receive the modified portions of the lead. In some cases, additional pressure devices, such as part of the housing of the pressure contact assembly, are used to facilitate the press-fitting operation.

FIGS.6A-6Care representative drawings of a pressure contact assembly600, according to exemplary embodiments.FIGS.6A-6Bare side views andFIG.6Cis a perspective view of the pressure contact assembly600. In exemplary embodiments, a power lead (terminal) has two portions602aand602b(collectively, “lead(s)602”), with lead portion602abeing orthogonal to lead portion602b, forming an “L shape”. The lead602is to be attached to a power substrate614consisting of a first surface608and a second surface612, with a ceramic tile610sandwiched therebetween. Once attached, lead portion602ais orthogonal to the power substrate614while lead portion602bis adjacent the power substrate614. In exemplary embodiments, the modification to the otherwise smooth surface of the lead portion602bis a coining u-shape604for attachment to the power substrate614.

Additionally, in exemplary embodiments, an over-etch606is cut into the power substrate614, specifically, the first surface608. The over-etch606is defined herein as a cut through the first surface608until the ceramic tile610is visible. Further, the over-etch606is wider at the bottom than at the top of the first surface608. In exemplary embodiments, the lead602is placed over the power substrate614until the coining u-shape604is disposed over the over-etch606. Pressure is applied to the lead portion602buntil the coining u-shape604fits into the over-etch606. Alternatively, the coining u-shape604may be slid into the over-etch606, from the back of the power substrate614or from the front. The first surface608will deform somewhat around the coining u-shape604, causing the lead602to be permanently attached to the power substrate614without using solder. The lead602is thus fastened to the power substrate614.

FIGS.7A-7Bare representative drawings of a pressure contact assembly700, according to exemplary embodiments.FIG.7Ais a perspective view andFIG.7Bis a side view of the pressure contact assembly700. Like the pressure contact assembly600, the pressure contact assembly700features a power lead (terminal) having two portions702aand702b(collectively, “lead(s)702”), with lead portion702abeing orthogonal to lead portion702b, forming an “L shape”. The lead702is to be attached to a power substrate714consisting of a first surface708and a second surface712, with a ceramic tile710sandwiched therebetween. In exemplary embodiments, the modification to the otherwise smooth surface of the lead portion602bis also a coining u-shape704for attachment to the power substrate714. An over-etch706is cut into the power substrate714until the ceramic tile710is visible.

In exemplary embodiments, lead portion702bfurther includes spring contacts716aand716b(collectively, “spring contact(s)716”). The spring contacts716are sections of the lead portion702bthat have been cut, then bent upward. In a non-limiting example, the cutout sections are generally rectangular in shape, forming the spring contacts716. In exemplary embodiments, housing718of the pressure contact assembly700pushes against the spring contacts716, thus providing constant pressure to the lead702, without need of solder. The lead702is thus fastened to the power substrate714.

FIGS.8A-8Care representative drawings of a pressure contact assembly800, according to exemplary embodiments.FIGS.8A-8Bare side views andFIG.8Cis a perspective view of the pressure contact assembly800. In exemplary embodiments, a power lead (terminal) has two portions802aand802b(collectively, “lead(s)802”), with lead portion802abeing orthogonal to lead portion802b, forming an “L shape”. The lead802is to be attached to a power substrate814consisting of a first surface808and a second surface812, with a ceramic tile810sandwiched therebetween. Once attached, lead portion802ais orthogonal to the power substrate814while lead portion802bis adjacent the power substrate814. In exemplary embodiments, the modification to the otherwise smooth surface of the lead portion802bis a button804for attachment to the power substrate814. The button804is an addition to the lead portion802b. In exemplary embodiments, the button804is a copper stud that is attached to a bottom surface of the lead portion802b, such as by laser welding.

In exemplary embodiments, an over-etch806is cut into the power substrate814, specifically, the first surface808. The over-etch806is cut through the first surface808until the ceramic tile810is visible. Further, the over-etch806is wider at the bottom than at the top of the first surface808. In exemplary embodiments, the lead802is placed over the power substrate814until the button804is disposed over the over-etch806. Pressure is applied to the lead portion802buntil the button804fits into the over-etch806. Alternatively, the button804may be slid into the over-etch806, from the back of the power substrate814or from the front. The first surface808will deform somewhat around the button804, causing the lead802to be permanently attached to the power substrate814without using solder. The lead802is thus fastened to the power substrate814.

FIGS.9A-9Care representative drawings of a pressure contact assembly900, according to exemplary embodiment.FIGS.9A-9Bare side views andFIG.9Cis a perspective view of the pressure contact assembly900. In exemplary embodiments, a power lead (terminal) has two portions902aand902b(collectively, “lead(s)902”), with lead portion902abeing orthogonal to lead portion902b, forming an “L shape”. The lead902is to be attached to a power substrate914consisting of a first surface908and a second surface912, with a ceramic tile910sandwiched therebetween. Once attached, lead portion902ais orthogonal to the power substrate914while lead portion902bis adjacent the power substrate914. In exemplary embodiments, the modification to the otherwise smooth surface of the lead portion902bis a deformation904in the top of the lead portion902b, which causes a protrusion916beneath the lead portion902b, where the protrusion916is for attachment to the power substrate914. The deformation904and protrusion916are extensions of the lead portion902b, which are achieved, in some embodiments, by coining, embossing, or blanking.

In exemplary embodiments, an over-etch906is cut into the power substrate914, specifically, the first surface908. The over-etch906is cut through the first surface908until the ceramic tile910is visible. Further, the over-etch906is wider at the bottom than at the top of the first surface908. In exemplary embodiments, the lead902is placed over the power substrate914until the deformation904and protrusion916are disposed over the over-etch906. Pressure is applied to the lead portion902buntil the protrusion916fits into the over-etch906. Alternatively, the protrusion916may be slid into the over-etch906, from the back of the power substrate914or from the front. The first surface908will deform somewhat around the protrusion916, causing the lead902to be permanently attached to the power substrate914without using solder. The lead902is thus fastened to the power substrate914.

FIGS.10A-10Dare representative drawings of a pressure contact assembly1000, according to exemplary embodiments.FIGS.10A-10Care side views whileFIG.10Dis a perspective view of the pressure contact assembly1000. In exemplary embodiments, a power lead (terminal) has two portions1002aand1002b(collectively, “lead(s)1002”), with lead portion1002abeing orthogonal to lead portion1002b, forming an “L shape”. The lead1002is to be attached to a power substrate1014consisting of a first surface consisting of two portions1008aand1008b(collectively, “first surface1008”) and a second surface1012, with a ceramic tile1010sandwiched therebetween. Once attached, lead portion1002ais orthogonal to the power substrate1014while lead portion1002bis adjacent the power substrate1014. In exemplary embodiments, the modification to the otherwise smooth surface of the lead portion1002bis the cutting away of a center portion (center cut) of the lead portion1002b, resulting in a pair of “feet”1020aand1020b(singularly, “foot1020”, collectively, “feet1020”) that are used to attach the lead1002to the power substrate1014.

In exemplary embodiments, over-etches1006aand1006b(collectively, “over-etch(es)1006”) are cut into the power substrate1014, specifically, the first surface1008. The over-etches1006are cut through the first surface1008until the ceramic tile1010is visible. Further, the over-etches1006are wider at the bottom than at the top of the first surface1008. In exemplary embodiments, the feet1020of the lead1002are slid into the power substrate1014until the foot1020afits into over-etch1006aand foot1020bfits into over-etch1006b.

The first surface1008of the power substrate1014has two parts, a first portion1008aand a second portion1008b. In exemplary embodiments, between the two over-etches1006aand1006bis an under-etch1016. The under-etch1016is defined herein as a cut into the first surface1008that does not reach the ceramic tile1010below. In this example, the under-etch1016is cut into the second portion1008bof the first surface. In contrast to the over-etches1006aand1006b, the under-etch1016is not cut all the way to the ceramic tile1010. A pressure device1018is shown, which could be a part of the housing of the pressure contact assembly1000. By applying pressure to the under-etch1016, the second portion1008bwill deform somewhat around the two feet1020of the lead1002, causing the lead1002to be permanently attached to the power substrate1014without using solder. In exemplary embodiments, as feet1020aand1020bare slid into respective over-etches1006aand1006b, mechanical pressure may be applied to the under-etch1016which deforms the second portion1008bof the first surface1008, resulting in a tight coupling of between the lead1002and the power substrate1014.

FIGS.11A-11Dare representative drawings of a pressure contact assembly1100, according to exemplary embodiments.FIGS.11A-11Care perspective views andFIG.11Dis a side view of the pressure contact assembly1100. In exemplary embodiments, a power lead (terminal) has two portions1102aand1102b(collectively, “lead(s)1102”), with lead portion1102abeing orthogonal to lead portion1102b, forming an “L shape”. The lead1102is to be attached to a power substrate1114consisting of a first surface1108and a second surface1112, with a ceramic tile1110sandwiched therebetween. Once attached, lead portion1102ais orthogonal to the power substrate1114while lead portion1102bis adjacent the power substrate1114. In exemplary embodiments, lead portion1102bis the portion of the lead1102being attached to the power substrate1114. In exemplary embodiments, the modification to the otherwise smooth surface of the lead portion1102bis an aperture1104cut through the lead portion1102b.

In exemplary embodiments, an under-etch1106and an over-etch1116are cut into the power substrate1114, specifically, the first surface1108. In some embodiments, the under-etch1116is a half-etch, meaning that half of the first surface1108is etched away. The under-etch1106is a rectangular cutout of the first surface1108that is not cut all the way to the ceramic tile1110, while the over-etch1116is cut through the first surface1108until the ceramic tile1110is visible. In a non-limiting example, the under-etch1106is rectangular while the over-etch1116is circular. Further, there is a circular portion1120of the first surface1108that is not etched between the under-etch1106and the over-etch1116. In exemplary embodiments, the circular portion1120is approximately the same diameter as the aperture1104.

In exemplary embodiments, the lead1102is disposed over the power substrate1114until the aperture1104fits over the circular portion1120. The dimension of the lead portion1102bis approximately the same as the dimension of the under-etch1106.

A pressure device1118is shown, which may be a part of the housing of the pressure contact assembly1100. By applying pressure to the over-etch1116, the circular portion1120will deform somewhat around the lead portion1102b, causing the lead1002to be permanently attached to the power substrate1114without using solder. In exemplary embodiments, as lead portions1102bis inserted into the into the under-etch1106, mechanical pressure may be applied to the over-etch1116which deforms the circular portion1120of the first surface1108, resulting in a tight coupling of between the lead1102and the power substrate1114.

Table 1 provides a comparison between materials used in power substrates versus using the pressure contact assemblies (400,500,600,700,800,900,1000, and1100). K88 is a leadframe manufacturer that uses copper and alloys to make the lead terminals both strong and flexible, resulting in a spring-like quality to the leads. Rthjc is the impedance from junction to case (outside surface of package). In exemplary embodiments, the leads for the above-described pressure contact assemblies400,500,600,700,800,900,1000, and1100are impregnated with a material to make the leads springier yet maintain hardness. Where lead frames typically have a hardness vector (HV) of 100 to 130, in exemplary embodiments, the pressure contact assemblies400,500,600,700,800,900,1000, and1100. Further, in exemplary embodiments, where prior art power substrates typically used Aluminum Oxide (Al2O3), Aluminum Nitride (AlN), or Zirconia Toughened Alumina (ZTA), the pressure contact assemblies400,500,600,700,800,900,1000, and1100utilize ceramic made of Si3N4(Silicon Nitride) for better performance rather than AlN.

TABLE 1Comparison between prior art and new technologyPrior artDisclosed artAdvantageUses industry standard softerUses K88 harder leadframeSturdy leadframe, hardcopper material likematerial (140~170 hardnesswearingTAMACA, KFC, 12Sn,value) or equivalent materialPMC90due to pressured contactrequirement when insertedinto power substrate cavityUses standard substrate Al203Uses high-performanceHigh current carryingor AlN DCBsubstrate, AMB Si3N4capability; no ceramic crackissue due to high bendingstrength and toughnessSoldered power terminalNo solder connectionHigh reliability performancedue to the absence of solder;high current carryingcapabilityPress fit pin to PCBPressured contact toDisclosed art is insideDCB/AMB/IMSpackage while prior art isoutside package

In exemplary embodiments, the ceramic tile used for the power substrate in the pressure contact assemblies400,500,600,700,800,900,1000,1100is modified from prior art power assemblies to enhance the strength of the power substrate. Table 2 provides characteristic data about the ceramic tile. In exemplary embodiments, thermal conductivity, bending strength, and fracture toughness are all considered when selecting the ceramic tile for the pressure contact assemblies400,500,600,700,800,900,1000,1100. In exemplary embodiments, the ceramic tiles are made using Silicon Nitride (Si3N4), also known as high-performance AMB substrate with a favorable combination to thermal conductivity, bending strength, and toughness, as compared to standard Al2O3, AlN, or ZTA. In addition, only AMB can achieve a thicker layer of copper to ceramic tile through brazing because, by “bonding process”, the proven thickness of the copper layer is only 0.50 mm maximum, as compared to AMB of 0.8 mm, which is ideal for a solderless connection to form the cavity (e.g., cavity422inFIGS.4A-4D) in the copper surface (e.g., first surface408of power substrate414).

While the present disclosure makes reference to certain embodiments, numerous modifications, alterations, and changes to the described embodiments are possible without departing from the sphere and scope of the present disclosure, as defined in the appended claim(s). Accordingly, it is intended that the present disclosure not be limited to the described embodiments, but that it has the full scope defined by the language of the following claims, and equivalents thereof.