Flip chip package for DRAM with two underfill materials

1. A microelectronic package, comprising:

a substrate having a first surface and a plurality of substrate contacts at the first surface;

a microelectronic element having a front surface and contacts arranged within a contact-bearing region of the front surface, the contact-bearing region entirely located within a middle third of a distance between first and second opposed edges of the front surface, the front surface having first and second peripheral regions between the contact-bearing region and the first and second opposed edges, the contacts facing the substrate contacts and joined thereto;

an underfill disposed between the substrate first surface and the contact-bearing region of the front surface of the microelectronic element, the underfill reinforcing the joints between the contacts and the substrate contacts, wherein the underfill does not contact the first and second peripheral regions; and

a joining material having a Young's modulus less than 75% of a Young's modulus of the underfill and bonding the substrate first surface with the front surface of the microelectronic element.

2. A microelectronic package as claimed in claim 1 , wherein the Young's modulus of the underfill is greater than 5 GPa, and the Young's modulus of the joining material is less than 5 GPa.

3. A microelectronic package as claimed in claim 1 , wherein the underfill is a different material than the joining material.

4. A microelectronic package as claimed in claim 1 , wherein the underfill is a no-flow underfill.

5. A microelectronic package as claimed in claim 1 , wherein the underfill is an epoxy having silica particles dispersed therein.

6. A microelectronic package as claimed in claim 1 , wherein the joining material includes at least one of an adhesive pad, a die attach adhesive, epoxy, and silicone.

7. A microelectronic package as claimed in claim 1 , wherein the joining material extends to a peripheral edge of the substrate.

8. A microelectronic package as claimed in claim 1 , wherein the joining material does not extend to a peripheral edge of the substrate.

9. A microelectronic package as claimed in claim 1 , wherein the joining material is disposed adjacent first and second opposed edges of the contact-bearing region.

10. A microelectronic package as claimed in claim 1 , further comprising an overmold region overlying a rear surface of the microelectronic element and the first surface of the substrate.

11. A microelectronic package as claimed in claim 1 , wherein the overmold region is a different material than both the underfill and the joining material.

12. A microelectronic package as claimed in claim 1 , wherein the overmold region is the same material as exactly one of the underfill and the joining material.

13. A microelectronic package as claimed in claim 1 , wherein the contact-bearing region is located adjacent a peripheral edge of the front surface of the microelectronic element.

14. A microelectronic package as claimed in claim 1 , wherein the microelectronic element embodies a greater number of active devices to provide memory storage array function than any other function.

15. A microelectronic package as claimed in claim 14 , wherein the microelectronic element includes a dynamic random access memory element.

16. A microelectronic package as claimed in claim 1 , wherein the microelectronic element is a first microelectronic element, the microelectronic package further including a second microelectronic element adjacent the first microelectronic element, the second microelectronic element having second contacts facing the substrate contacts and joined thereto.

17. A microelectronic package, comprising:

a substrate having a first surface and a plurality of substrate contacts at the first surface;

a microelectronic element having a front surface and contacts arranged within a contact-bearing region of the front surface, the contacts facing the substrate contacts and joined thereto;

an underfill disposed between the substrate first surface and the contact-bearing region of the front surface of the microelectronic element, the underfill reinforcing the joints between the contacts and the substrate contacts; and

a joining material having a Young's modulus less than 75% of a Young's modulus of the underfill and bonding the substrate first surface with the front surface of the microelectronic element,

wherein the substrate has a second surface opposite the first surface and further includes at least one aperture extending between the first and second surfaces, the underfill extending within the at least one aperture.

18. A microelectronic package as claimed in claim 17 , wherein the contact-bearing region is entirely located within a middle third of a distance between first and second opposed edges of the front surface of the microelectronic element, and wherein the at least one aperture overlies at least a portion of the contact-bearing region.

19. A microelectronic package as claimed in claim 17 , wherein the contacts are arranged in parallel rows.

20. A microelectronic package as claimed in claim 19 , wherein the contacts are arranged in at least two parallel rows, at least one of the apertures extending between adjacent parallel rows of the substrate contacts joined to the contacts.

21. A microelectronic package as claimed in claim 1 , wherein the substrate consists essentially of a material having a coefficient of thermal expansion in a plane of the substrate of less than 30 ppm/° C.

22. A microelectronic package as claimed in claim 1 , further comprising terminals exposed at a second surface of the substrate for interconnection with at least one external component.

23. A microelectronic package as claimed in claim 22 , wherein the substrate further includes a plurality of conductive vias extending between the first and second surfaces of the substrate, the conductive vias being electrically connected with at least some of the substrate contacts and at least some of the terminals.

24. A microelectronic package as claimed in claim 22 , further comprising a plurality of electrically conductive joining units attached to the terminals, the joining units configured for joining the microelectronic package with the at least one external component.

25. A module including a plurality of microelectronic packages according to claim 1 , the module having a circuit panel for transport of signals to and from each of the microelectronic packages.

26. A system comprising a microelectronic package according to claim 1 and one or more other electronic components electrically connected to the microelectronic package.

27. A system as claimed in claim 26 , wherein at least one of the other electronic components is a circuit panel.

28. A system as claimed in claim 26 , further comprising a housing, said microelectronic package and said other electronic components being mounted to said housing.

29. A microelectronic package as claimed in claim 17 , wherein the front surface of the microelectronic element further includes first and second peripheral regions between the contact-bearing region and first and second opposed edges of the front surface of the microelectronic element, and the underfill does not contact the first and second peripheral regions.

30. A microelectronic package as claimed in claim 17 , wherein the contact-bearing region extends up to one-third of a distance between first and second opposed edges of the front surface of the microelectronic element.

31. A microelectronic package as claimed in claim 30 , wherein the contact-bearing region is entirely located within a middle third of a distance between the first and second opposed edges of the front surface of the microelectronic element.

32. A microelectronic package as claimed in claim 31 , wherein the joints between the contacts and the substrate contacts include at least one of solder balls and conductive pillars.

33. A microelectronic package as claimed in claim 32 , wherein the underfill surrounds the joints in the contact-bearing region.