Selective Soldering with Photonic Soldering Technology

Electronic assembly methods and structures are described. In an embodiment, an electronic assembly method includes bringing together an electronic component and a routing substrate, and directing a large area photonic soldering light pulse toward the electronic component to bond the electronic component to the routing substrate.

BACKGROUND

Field

Embodiments described herein relate to microelectronic packaging techniques, and more particularly to photonic soldering.

Background Information

Microelectronic packaging has widely adopted soldering technology for bonding of electronic components. In a widely adopted conventional wide area soldering process, a bonding substrate and all components being bonded thereto are all heated above a solder reflow temperature. Such mass reflow may require that all materials can withstand the solder reflow temperature (e.g. greater than 215° C.) and dwell time, often on the order of minutes. Additional considerations with mass reflow include solder extrusion for underfilled electronic components. Selective soldering techniques such as laser soldering and hot air soldering have been adopted in some applications to avoid high temperature exposure, for example to the electronic component being bonded, the substrate, or adjacent components.

More recently large area photonic soldering has been proposed as a method for soldering chips to a low temperature substrate. In such a method a high-power flash lamp (e.g. xenon) is pulsed to emit a high intensity flash pulse that is selectively absorbed by the chips being bonded rather than the bonding substrate.

SUMMARY

Electronic assembly methods and structures are described. In an embodiment, an electronic assembly method includes bringing together an electronic component and a routing substrate, and directing a large area photonic soldering light pulse toward the electronic component to bond the electronic component to the routing substrate. A variety of structures are described that may shield a sensitive electronic component from exposure to the light pulse. The disclosed assembly methods may additionally be applied to joining of routing substrates.

DETAILED DESCRIPTION

Embodiments describe selective soldering techniques with photonic soldering, and associated structures. The selective soldering processes may restrict photonic light transmission to select areas, and leverage different light energy absorption rates of different materials.

It has been observed that traditional selective soldering techniques such as laser soldering and hot air soldering have associated challenges in implementation. For example, it can be difficult to control molten solder temperature with laser soldering, which can also damage components. Additionally, laser soldering is pad by pad, and has a low throughput of units per hour (UPH). Hot air soldering additionally has the associated issues of air control, and low UPH.

The selective soldering methods and structures in accordance with embodiments may allow use of low temperature materials, such as polyethylene terephthalate (PET) flex substrates, with high temperature solder, and minimize heat impact on adjacent components. The selective soldering methods and structures in may also allow for large area (e.g. wafer or panel level) selective soldering with short time (on the order of seconds). Furthermore, the selective soldering methods and structures described herein can be implemented with a variety of electrically conductive bonding materials that are heat activated including namely solder materials, as well as sintering pastes (e.g. silver paste, copper paste), a snap cure material, conductive epoxy, etc. Furthermore, the selective soldering methods and structures may allow for the use of bonding materials with high activation temperatures (such as a high temperature solder with a liquidus temperature above 217° C.) in combination with sensitive electronic components or routing substrates that need to be maintained below the high activation temperature (e.g. solder reflow, sintering, cure).

Referring now toFIG. 1a flow chart is provided of an electronic assembly method including selective photonic soldering in accordance with an embodiment. In interest of conciseness and clarity, the sequence ofFIG. 1is discussed concurrently with the cross-sectional side view illustrations ofFIGS. 2-4. Specifically,FIG. 2illustrates selective photonic soldering of an electronic component130such as a device180to a transparent routing substrate110,FIG. 3illustrates selective photonic soldering of an electronic component130such as a transparent routing substrate190to an opaque routing substrate110, andFIG. 4illustrates selective photonic soldering of a transparent electronic component130such as device180to a routing substrate110in accordance with embodiments.

The electronic components130in accordance with all embodiments described herein may be a variety of devices180including chips, packages, diodes, sensors, including both active and passive devices, and routing substrates190such as rigid or flexible routing substrates. Essentially, embodiments may be applicable to any pad-to-pad connection. Referring briefly to the embodiment illustrated inFIG. 9, such a selective soldering technique is utilized to join a lid900to a routing substrate110where the lid900also functions to block light transmission to the electronic component130that the lid covers.

Referring again toFIG. 1, in an embodiment an electronic assembly method includes bringing together an electronic component130and a routing substrate110with a heat activated bonding material140located in a shadow of the electronic component between the electronic component130and the routing substrate110at operation1010. Exemplary heat activated bonding materials140in accordance with embodiments described herein include solder materials (e.g. solder bumps), as well as sintering pastes (e.g. silver paste, copper paste), a snap cure material, conductive epoxy, etc. As described herein, in an exemplary top view illustration the shadow is represented by the are defined by the outline (perimeter) of the electronic component130overlapping the routing substrate110. Thus, the area directly between the electronic component130and routing substrate110would be within the shadow of the electronic component130. At operation1020, a light pulse150is directed from a light source and transmitted through the routing substrate110or the electronic component130to activate (e.g. reflow, sinter, cure) the bonding material140.

In the embodiment illustrated inFIG. 2, the light pulse150is transmitted through a bottom side114of the routing substrate110and toward the bonding material140to activate the bonding material. As shown, the routing substrate110includes a top side112and bottom side114. The electronic component130includes a top side132and bottom side134. The routing substrate110may further include a transparent layer120, a plurality of metal landing pads116on a top side121of the transparent layer120. Additional routing layers may be including on the top side121of the transparent layer120or within the transparent layer120. The bonding material140is a plurality of high temperature solder bumps in an embodiment. The routing substrate110may additionally include a coverlay film122on the top side121of the transparent layer120, and a plurality of openings124in the coverlay film122exposing the plurality of metal landing pads116on the top side121of the transparent layer120. The coverlay film122may be formed of a suitable insulating material such as polymer or oxide. For example, the coverlay film122may be a soldermask material, such as epoxy.

The electronic assembly methods in accordance with embodiments may utilize large area, yet localized photonic soldering techniques to allow for high temperature soldering (e.g. solder materials with a liquidus temperature above 217° C.) of sensitive electronic components (e.g. components that need to be maintained below the high temperature solder reflow temperature). Thus, the particular configurations may isolate the electronic components from the heat. Still referring toFIG. 2, the coverlay film122may be designed to substantially block transmission of the light pulse150toward the electronic component130by absorption or reflection. Thus, the light pulse is substantially absorbed or reflected in the shadow of the electronic component130. However, the light pulse that is transmitted to the landing pads116is absorbed by the landing pads, and being a thermally conductive metallic material heat is transferred to the bonding material140to join the landing pads116of the routing substrate110to the metal contact pads136of the electronic component130.

As used herein, the phrases “substantially block,” “substantially absorb,” “substantially reflect” or be “substantially transparent” to transmission of the photonic soldering light pulse are used in a general sense to characterize some non-bonding layer materials considering the photonic soldering techniques employed. For example, a feature that substantially blocks transmission of the photonic soldering light pulse, may block greater than 90% of the photonic soldering light pulse by absorption or reflection. A feature that is substantially transparent may transmit greater than 90% of the photonic soldering light pulse. In some embodiments, the photonic soldering light pulse may be in the ultraviolet-infra red (UV-IR) spectrum, though embodiments are not necessarily limited to this range and can vary based on absorption rate of selected materials. Blocking of the photonic soldering light pulse150transmission may be substantial enough so that the electronic component is not heated to same temperature required for activation (e.g. reflow, sintering, cure) of the bonding material140. In some embodiments, the bonding material140(e.g. black solder paste, black solder ball) may additionally be designed for absorption photonic soldering light pulse150.

In accordance with some embodiments a coverlay film122serves as a light mask to substantially block the light pulse. In an embodiment, the coverlay film122is characterized as a light absorbing or opaque material to substantially block/absorb transmission (e.g. greater than 90%) of the light pulse. For example, the light absorbing material can be a dark color, such as black. Furthermore, the coverlay film122may be an insulating material with low thermal conductivity, so that heat is not transferred as efficiently as with the metal landing pads. The light absorbing material may be further characterized as having no or low (e.g. less than 10%) light reflectance. Conversely, the coverlay film122may be characterized as a reflective material to substantially block/reflect (e.g. greater than 90%) of the light pulse. For example, the light pulse may be reflected back toward and through the transparent layer (e.g. substrate)120. Reflection may be substantial enough so that the electronic component is not heated to same temperature required for activation of the bonding material140. In an embodiment, the reflective material is a light color, such as white.

In an embodiment, an electronic assembly100includes an electronic component130, a routing substrate110including a top side112and a bottom side114, where the top side112of the routing substrate110includes a plurality of metal landing pads116. A bonding material140is located in a shadow of the electronic component130between the electronic component and the routing substrate110. In various embodiments, either the electronic component130or the transparent layer120is substantially transparent to a photonic soldering light pulse150. The routing substrate may include a coverlay film122and a plurality of openings124in the coverlay film exposing the plurality of metal landing pads116. The coverlay film122may cover an entirety of the shadow of the electronic component130between the electronic component and the routing substrate110, less the plurality of openings124exposing the plurality of metal landing pads116. This may facilitate substantially blocking the photonic soldering light pulse150wavelength, which may additionally be facilitated by materials selection and doping/color of the coverlay film122. In an embodiment, the coverlay film122(e.g. black film) substantially blocks/absorbs a photonic soldering light pulse. In an embodiment, the coverlay film122(e.g. white film) substantially blocks/reflects a photonic soldering light pulse.

Referring now toFIG. 3, in the embodiment illustrated the light pulse150may be directed through a top side132of the electronic component130and toward the bonding material140to activate (e.g. reflow, sinter, cure) the bonding material. In such an embodiment, the body of the electronic component130is substantially transparent to the light pulse. In this response, substantially transparent allows sufficient transfer of the light pulse150through the body of electronic component130to activate (e.g. reflow, sinter, cure) the bonding material140. As shown, the electronic component130may include a metal contact pad136which will selectively absorb the light pulse150, and transfer heat to the bonding material140for activation (e.g. reflow, sinter, cure). In the particular embodiment illustrated, the electronic component130is a transparent routing substrate190. Thus, the illustrated embodiment joints two routing substrates, which may be rigid or flexible. In an embodiment, the electronic component130of the electronic assembly100is a second routing substrate190that is substantially transparent to the photonic soldering light pulse.

FIG. 4illustrates an embodiment including a transparent device180as the electronic component130. In an exemplary implementation the device180is formed of a silicon body, which may be thin enough (e.g. less than 200 μm) to be substantially transparent to the light pulse150. In an embodiment, the electronic component130of the electronic assembly100is a silicon device less than 200 μm thick, which is transparent to the photonic soldering light pulse.

Referring now toFIG. 5a flow chart is provided of an electronic assembly method including selective photonic soldering with aid of an exposed portion of a thermally conductive material in accordance with an embodiment. In interest of conciseness and clarity, the sequence ofFIG. 5is discussed concurrently with the cross-sectional side view illustrations ofFIGS. 6A-12C. In an embodiment an electronic assembly method includes bringing together an electronic component130and a routing substrate110at operation5010, and directing a light pulse150from a light source toward a portion of a thermally conductive material located outside of a shadow of the electronic component130between the electronic component and the routing substrate110at operation5020. The thermally conductive material may be a variety of structures in accordance with embodiments, such as metal wiring layer of the routing substrate (including routing layers and/or metal landing pads), metal wiring layer attached to the routing substrate, a wire for wire bonding, lid, etc. At operation5030thermal energy is transferred through the thermally conductive material to the bonding material to activate the bonding material, which forms an electrically conductive solder joint between the electronic component130and the routing substrate110.

FIG. 6Ais a cross-sectional side view illustration of selective photonic soldering of an electronic component130to a routing substrate110with a metal wiring layer650outside the shadow of the electronic component in accordance with an embodiment. The metal wiring layer650may be part of the routing substrate110. For example, the metal wiring layer650may include a portion118that spans outside of the shadow of the electronic component, and portion (e.g. metal landing pad116) that spans within the shadow of the electronic component. Portion118may be part of a metal routing, or extension of the metal landing pad116. Similarly, the bonding material140may be located in the shadow of the electronic component, and may optionally span outside of the shadow of the electronic component on the portion118of the metal wiring layer650. Where bonding material140additionally spans outside of the shadow a pigment may optionally be added into the bonding material140to facilitate light absorption by the boding material140in addition to the metal wiring layer650. In order to protect a sensitive electronic component130from the light pulse150, a light mask600can be placed over the electronic component130when directing the light pulse150from the light source toward the exposed portion of the thermally conductive material located outside of the shadow of the electronic component130. In such an embodiment, the light mask600can be formed of a material to absorb the light pulse, and include openings to pass the light pulse. Referring now toFIG. 6Ban alternative version of a light mask is illustrated in which the light mask600includes a bulk layer602that is at least substantially transparent to the light pulse150, and a patterned filter layer604. The patterned filter layer604may reflect the light pulse150and/or absorb the light pulse150in order to filter transmission. In an embodiment the bulk layer is formed of glass (e.g. quartz), or a transparent polymer. In an embodiment, the patterned filter layer604includes one or more metal layers that can be deposited using various suitable thin film deposition techniques. This can additionally take advantage of the reflectivity of the metallized coating (e.g. aluminum, gold, silver) in conjunction with un ultraviolet filter already integrated into a light source housing assembly to effectively block any incoming light to be filtered. In the illustrated embodiment, the light mask600can be pressed on top of the electronic component130to ensure sufficient force is present for photonic soldering to the routing substrate110. The light mask600may also selectively heat the electronic component and routing substrate using the (metallized) patterned filter layer604. Such light masks600as described and illustrated with regard toFIGS. 6A-6Bmay additionally be used in other embodiments described herein, although not specifically illustrated.

FIG. 7is a cross-sectional side view illustration of selective photonic soldering of an electronic component to a routing substrate with an external wire in accordance with an embodiment. In the embodiment illustrated inFIG. 7, the wiring layer700may be similar to wiring layer650, with one difference being the wiring layer700extends beyond an outside perimeter111of the routing substrate110. In an embodiment, wiring layer700is a separate structure bonded to the routing substrate110. In one implementation, the electronic assembly100ofFIG. 7is a wearable structure, where the electronic component130and routing substrate110are embedded in a textile (e.g. fabric), with leads of the wiring layer700extending therefrom. In this configuration, the exposed leads that are either outside the shadow of the electronic component130, or extend outside of the textile710absorb the light pulse150from the light source and transfer the heat to the bonding material140. Similar toFIGS. 6A-6B, a light mask600can optionally be used.

FIG. 8Ais a cross-sectional side view illustration of selective photonic soldering of an exposed metal wire800in accordance with an embodiment. In the particular embodiment illustrated, the electronic component130is attached face up to the routing substrate110using an adhesive layer802. The bonding material140is used for wire bond attachment. For example, the bonding material140can include a first solder bump and a second solder bump, and the metal wire is bonded to the top side132of the electronic component130with the first solder bump, and a top side112of the routing substrate110with the second solder bump. Alternatively, other bonding materials may be used in lieu of solder bumps. In such a configuration, the wire800is directly exposed to the light pulse, and transfers heat to the bonding material140.

Referring now toFIG. 8B, a cross-sectional side view illustration is provided of selective photonic soldering of a printed interconnect850in accordance with an embodiment. For example, a printed interconnect850may be printed (e.g. ink jet, screen print, etc.) onto a thin device180, such as less than30microns thick, and routing substrate110. A light pulse150is then directed toward the printed interconnect850to activate the printed interconnect (e.g. simultaneously flow, cure) to form the electrical joint between the landing pads116and contact pads136. The structure and process ofFIG. 8Bmay or may not include a separate bonding material for formation.

Thus far a variety of thermally conductive materials (e.g. wiring layers, wires) have been described for transferring heat to activate a bonding layer for bonding an electronic component130to a routing substrate110. In addition,FIG. 8Bhas described using such a photonic soldering technique to flow, cure a printed interconnect850, which directly absorbs the light energy. Referring now toFIG. 9, a cross-sectional side view illustration is provided of selective photonic soldering of a lid900to a routing substrate110in accordance with an embodiment. In such an embodiment, the thermally conductive material is a lid900, and bonding material140is located between the lid and the routing substrate110and directly physically connects the lid to the routing substrate. Furthermore, the lid900may shield an underlying sensitive electronic component130from the light pulse150. Similar to other embodiments, a light mask600may be used to shield adjacent electronic components130. In the embodiment illustrated inFIG. 9the lid900is selectively heated, and the heat is transferred to the bonding material140to complete the lid900attachment. Furthermore, the lid900can protect the underlying electronic component130from shorting, particularly if there happens to be a void in the underfill material135. In an embodiment., slots902can be formed in locations of the base or feet of the lid904which will be placed directly over the bonding material140in order allow direct absorption of the light pulse150by the bonding material140.

Each of the embodiments described and illustrated thus far have also illustrated a photonic soldering technique of a single electronic component or lid, on a single side of the routing substrate110. However, embodiments are not so limited and may be applicable to double sided integration, and stacking of components.FIG. 10Ais a cross-sectional side view illustration of double sided selective photonic soldering of electronic components130to a routing substrate110with a backside conductive material in accordance with an embodiment. WhileFIG. 10Ais substantially similar to that ofFIGS. 6A-6B, this is exemplary, and double sided selective photonic soldering may be applied to the other illustrated configurations as well. Furthermore, the selective photonic soldering techniques may cover a large area, and multiple electronic components and routing substrates.

Each of the embodiments illustrated and described with regard toFIGS. 6A-10Ahave shared a common feature of selective photonic soldering with aid of an exposed portion of a thermally conductive material. The light pulses150have generally been directed towards top sides of the electronic components130and routing substrates110, where the exposed portions of the thermally conductive material have been outside of the shadow between the electronic components130and routing substrates110, or even on top of the electronic components130.

Referring now toFIGS. 10B-10Ccross-sectional side view illustrations are provided for an electronic assembly100formed by selective photonic soldering of an electronic component130onto a metal wiring layer bridge109B in accordance with embodiments.FIG. 10Dis a schematic top-down illustration of the electronic assemblies ofFIGS. 10B-10Cin accordance with an embodiment. As show, the electronic assembly100may include a routing substrate110including one or more dielectric layers107and conductive routing layers109. The routing substrate110includes an opening105in a bulk area101(e.g. through the dielectric layers107). A metal wiring layer bridge109B extends from the bulk area101and into the opening105, and includes a plurality of landing pads116onto which a component130is bonded.

Similar to the metal wiring layers650,700, the metal wiring layer bridge109B may include a portion118that spans outside the shadow of the electronic component130, and a portion (e.g. metal landing pads116) that span within the shadow of the electronic component. Similarly, the bonding materials140may be located in the shadow of the electronic component130. Portion118spanning outside of the shadow of the electronic component130may be useful when directing the light pulse150from above the electronic component and a top side off the routing substrate110as shown inFIG. 10B. Alternatively, or additionally, the light pulse150can be directed form a back side of the routing substrate110opposite the electronic component to transfer head through the metal wiring layer bridge109B.

Referring toFIG. 10Dthe metal wiring layer bridge109B may include a plurality of metal wiring arms119extending from the bulk area101and into the opening105For example, each arm119can include a landing pad116, and a portion118which may optionally extend outside the shadow of the component130,180. The particular cut-out configuration ofFIGS. 10B-10Din which the electronic component130is bonded to a metal wiring layer bridge109B may allow for a photonic soldering technique that incorporates a sensitive, low temperature routing substrate110materials (e.g. dielectric layers107such as PET) and can also allow for use of high temperature solder (e.g. characterized by a liquidus temperature above 217° C.). Furthermore, where electronic component130may be sensitive to the light pulse, area of the wiring layer bridge109B (including landing pads116, and any dummy structure) may be increased to block light transmission.

In an embodiment, an electronic assembly method includes bringing together an electronic component130and a routing substrate110, directing a light pulse150from a light source toward a portion of a thermally conductive material (e.g. wiring layer bridge109B) located outside a shadow of the electronic component and the routing substrate110. For example, this may be a portion118of the wiring layer bridge109B laterally adjacent to the shadow, or toward a back side of the wiring layer bridge109B. Thermal energy is then transferred through the thermally conductive material (wiring layer bridge109B) to a bonding material140to activate the bonding material and bond the electronic component130to the routing substrate110, or more specifically to landing pads116of the wiring layer bridge109B. Similar to the description ofFIGS. 6A-6B, a light mask600can be located over the electronic component130when directing the light pulse150toward the wiring layer bridge109B.

FIG. 11is a cross-sectional side view illustration of selective photonic soldering of an electronic component130to a routing substrate110with a backside conductive material in accordance with an embodiment. Specifically, the thermally conductive material includes a via opening160with sidewalls164extending through the routing substrate110, and the light pulse150is directed toward a bottom side114of the routing substrate110, and the bonding material140is located on a top side112of the routing substrate110and physically connects the electronic component to the top side of the routing substrate. In an embodiment, the conductive material includes a landing pad116, via opening160, and bottom contact area166. The bottom contact area166may additionally be sized to absorb the light pulse150, or partially block transmission of the light pulse through the routing substrate110. Routing substrate110may additionally be opaque to the light pulse150to prevent transmission of the light pulse150to a sensitive electronic component130. Such a thermally conductive material, including the via opening160and bottom contact area166may optionally be integrated in the structure ofFIG. 2to facilitate heat conduction.

FIG. 12Aa cross-sectional side view illustration of selective photonic soldering of an electronic component130(e.g. device180or routing substrate190) to a routing substrate110by transferring heat through circuitry in the electronic component in accordance with an embodiment. The embodiment illustrated inFIG. 12Ais similar to that illustrated inFIG. 11in that a conductive path is used to transfer heat through a substrate. In the embodiment illustrated inFIG. 12A, heat is transferred through circuitry in the electronic component130, which need not be transparent and may be transparent or opaque, and rigid or flexible. As shown, the electronic component is bonded to the routing substrate110with a bonding material140that connects landing pad116and metal contact pad136. The contact pad136is electrically connected to an absorption pad138on an opposite side of the electronic component130. In the illustrated embodiment, this corresponds to the top side132, and the circuitry connects the top side132to bottom side134of the electronic component. The circuitry connecting the absorption pad138to the contact pad136may include one or more vias139and routing layers196. A shown, a photonic soldering technique may include placing a light mask600over the electronic component130such that the light pulse150is selectively directed to, and absorbed by the absorption pads138, which transfer heat through the circuitry to contact pad136, and hence bonding material140to activate the bonding material. Other configurations are also possible. For example, if the electronic component130is transparent, the openings in the light mask600can also expose the contact pad(s)136and intermediate circuitry (vias139, routing layers196) such that selection portions of the circuitry are absorb the light pulse150and transfer heat. A coverlay film123may optionally be placed over the side of the electronic component (e.g. top side132) including absorption pad(s)138to provide insulation and/or mechanical protection. In an embodiment, the coverlay film123is formed of transparent material, to facilitate transfer and absorption of the light pulse150. In such a configuration, the absorption pad138is not populated with a bonding material, and thus appears open. Referring briefly toFIG. 12Can alternative embodiment of a light mask600is illustrated similar to that previously described and illustrated with regard toFIG. 6B. As a distinction, the patterned filter layer604inFIG. 12Cmay be patterned to include openings605to selectively pass the light pulse150to the component130. In an embodiment, the light mask600can be pressed on the electronic component130when directing the light pulse150from the light source toward the absorption pad138on the top side132of the electronic component130. For example, the light mask600may have an opening605in a patterned filter layer604aligned (directly) over the absorption pad138and between the light source and the absorption pad138.

In some instances, the electronic component130may have a large metal (e.g. copper) plane formed in one of the routing layers196. For example, such a metal plane may correspond to a ground or power plane formed in the circuitry. Referring now to the top view illustration inFIG. 12B, in order to isolate the heat path, and guide the heat down to the bonding material140instead of across the metal plane199, a via pad195may be thermally isolated from the metal plane199by openings197partially surrounding the via pad195within the routing layer196. Tie bars198may connect the via pad195to the adjacent metal plane199in the routing layer196to maintain electrical connection, while mitigating lateral heat transfer.

In an embodiment, an electronic assembly method includes directing a light pulse150from a light source toward an absorption pad(s)138on a top side132of an electronic component130, and transferring thermal energy from the absorption pad138through circuitry located in the electronic component to the bonding material140to activate he bonding material. In an embodiment, an electronic assembly100includes an electronic component130including a top side132and a bottom side134, where the top side132of the electronic component includes an absorption pad(s)138, the bottom side134of the electronic component includes a contact pad(s)136, and circuitry connects the absorption pad to the landing pad. The electronic assembly further includes a routing substrate110including a top side112and a bottom side114, where the top side112of the routing substrate includes one or more metal landing pads116. A bonding material140is located in a shadow of the electronic component between the electronic component130and the routing substrate110. The bonding material140may be located on the one or more metal landing pads116, and join the one or more metal landing pads116to the contact pad(s)136. A coverlay film123can be located on the top side132of the electronic component and covering the absorption pad(s)138. For example, the absorption pad(s)138may not be not populated. The circuitry that connects the absorption pad(s)138to the contact pad(s)136may optionally include a routing layer196that includes a via pad195that is electrically connected to a metal plane199with one or more tie bars198and physically separated from the metal plane199with one or more openings197around the via pad195.

Referring now toFIG. 13a flow chart is provided of an electronic assembly method including selective photonic soldering through a via opening in accordance with an embodiment. In interest of conciseness and clarity, the sequence ofFIG. 13is discussed concurrently with the cross-sectional side view illustrations ofFIGS. 14A-15D. In an embodiment an electronic assembly method includes bringing together an electronic component and a routing substrate at operation1310, and directing a light pulse150from a light source toward a portion of a bonding material140located outside of a shadow of the electronic component130between the electronic component and the routing substrate110at operation1320. At operation1330the bonding material140is activated through a via opening located in the electronic component or the routing substrate to bond the electronic component to the routing substrate.

Referring toFIG. 14A, the via opening160is located in the routing substrate110. A thermally conductive (e.g. metal) liner162can optionally line the via opening160sidewalls, and optionally the top or bottom sides of the routing substrate. The thermally conductive liner162can be formed using a suitable deposition technique (chemical vapor deposition, evaporation, sputtering) or laser direct structuring where a metallic inorganic compound is activated by laser. Thus, the thermally conductive liner162may include a metal layer of a metallic inorganic compound included in the dielectric layer(s) of the routing substrate110.

In the illustrated embodiment, the light pulse150is directed toward a bottom side114of the routing substrate110, and the electronic component130is on the top side112of the routing substrate110. The routing substrate110may optionally be opaque the light pulse150to block transmission to a sensitive electronic component130. In accordance with embodiments, the light pulse150activates (e.g. reflow, sintering, curing) the bonding material140through the via opening160for bonding. In a particular embodiment, this may be solder material reflow.

FIGS. 14B-14Dare close-up cross-section side view illustration of a solder material location prior to reflow in accordance with embodiments. The bonding material140in accordance with embodiment may be formed of a variety of suitable materials, such as solder (e.g. low temperature or high temperature) and may be a variety of suitable shapes, including solder balls and other preforms, such as cylinders, blocks, t-shape preforms etc. In the embodiment illustrated inFIG. 14Bthe bonding material140is applied to, or “bumped” over the via opening160on the bottom side114of the routing substrate110opposite the component130,180. In the embodiment illustrated inFIG. 14Cthe bonding material140can be applied to the via opening160on the top side112of the routing substrate110or to the contact pad136of the component130. In the embodiment illustrated inFIG. 14Dthe bonding material140can be placed inside the via opening160, or onto the contact pad136. In the particular embodiment illustrated, the bonding material140in the shape of a cylinder or block but may also have other shapes, including t-shape as illustrated inFIG. 15D.

Upon ceasing application of the light source, the bonding material140may solidify to form a joint in which the bonding material substantially fills the via opening160and is at least partially located on the bottom side114of the routing substrate110.

A similar processing technique may be utilized for bonding of routing substrates to one another.FIG. 15Ais a cross-sectional side view illustration of selective photonic soldering routing substrates by reflowing solder material through a via opening170located in an electronic component130such as a second routing substrate190in accordance with an embodiment. Similarly, a thermally conductive (e.g. metal) liner172can optionally be located on the via opening170sidewalls174, and optionally the top or bottom sides132,134of the second routing substrate190. The thermally conductive liner172can be formed using a suitable deposition technique (chemical vapor deposition, evaporation, sputtering) or laser direct structuring where a metallic inorganic compound is activated by laser. Thus, the thermally conductive liner172may include a metal layer of a metallic inorganic compound included in the dielectric layer(s) of the component130(which may be a second routing substrate190). As shown, the light pulse150is directed toward the top side132of the second routing substrate190, and a bottom side134of the second routing substrate is bonded to the routing substrate110. The routing substrate110and second routing substrate190may be a variety of configuration of rigid or flexible substrates, or transparent or opaque to the light pulse150.

FIGS. 15B-15Dare close-up cross-section side view illustration of a solder material location prior to reflow in accordance with embodiments. The bonding material140in accordance with embodiment may be formed of a variety of suitable materials, such as solder (e.g. low temperature or high temperature) and may be a variety of suitable shapes, including solder balls and other preforms, such as cylinders, blocks, t-shape preforms etc. In the embodiment illustrated inFIG. 15Bthe bonding material140is applied to, or “bumped” over the via opening170on the top side132of the electronic component130(which may be a second routing substrate190) opposite the routing substrate110. In the embodiment illustrated inFIG. 15Cthe bonding material140can be applied to the via opening170on the bottom side134of the component130(which may be a second routing substrate190) or to the top side112of the routing substrate110. In the embodiment illustrated inFIG. 15Dthe bonding material140can be placed inside the via opening170, or onto the routing substrate110. In the particular embodiment illustrated, the bonding material140is a t-shape but may also have other shapes, including cylinder, block, etc.

Upon ceasing application of the light source, the bonding material140may solidify to form a joint in which the bonding material substantially fills the via opening170and is at least partially located over the top side132of the second routing substrate190(or electronic component) and under the bottom side134of the second routing substrate190(or electronic component).

In utilizing the various aspects of the embodiments, it would become apparent to one skilled in the art that combinations or variations of the above embodiments are possible for selective photonic soldering. Although the embodiments have been described in language specific to structural features and/or methodological acts, it is to be understood that the appended claims are not necessarily limited to the specific features or acts described. The specific features and acts disclosed are instead to be understood as embodiments of the claims useful for illustration.