Reversed build-up substrate for 2.5D

An assembly, comprising:

• one or more microelectronic elements;
• a circuit structure made of a plurality of dielectric layers and electrically conductive features thereon, the circuit structure having front and rear opposite surfaces and a maximum thickness of less than 30 microns in a direction normal to the front surface,
• the electrically conductive features comprising front contacts at the front surface electrically coupled with the one or more microelectronic elements, the front contacts facing and joined with corresponding contacts of the one or more microelectronic elements, rear conductive elements at the rear surface, and first conductive traces having maximum widths less than five microns, the front contacts electrically coupled with the rear conductive elements through the first traces;
• and
• a substrate defining a first surface laminated onto the rear surface of the circuit structure and a second surface opposite therefrom, the substrate comprising a dielectric element and having terminals at the second surface, the dielectric element defining the first surface,
• the dielectric element having first conductive elements facing the rear conductive elements and joined thereto, and second conductive traces electrically coupled to the first conductive elements and extending in directions parallel to the first surface, at least some of the second traces having maximum widths greater than five microns.

An assembly, comprising:

• a circuit structure made of a plurality of dielectric layers and electrically conductive features thereon, the circuit structure having front and rear opposite surfaces and a maximum thickness of less than 30 microns in a direction normal to the front surface,
• the electrically conductive features comprising front contacts at the front surface configured for joining with corresponding contacts of one or more microelectronic elements, rear conductive elements at the rear surface, and first conductive traces having maximum widths less than five microns, the front contacts electrically coupled with the rear conductive elements through the first traces;
• a substrate defining a first surface laminated onto the rear surface of the circuit structure and a second surface opposite therefrom, the substrate comprising a dielectric element and having terminals at the second surface, the dielectric element defining the first surface,
• the dielectric element having first conductive elements facing the rear conductive elements and joined thereto, and second conductive traces electrically coupled to the first conductive elements and extending in directions parallel to the first surface, at least some of the second traces having maximum widths greater than five microns;
• and
• a circuit panel having panel contacts at a surface thereof, the substrate being joined with the circuit panel, the terminals of the substrate being electrically coupled with the panel contacts.