Browse Prior Art Database

Multiple Substrate Packages

IP.com Disclosure Number: IPCOM000126178D
Original Publication Date: 2005-Aug-10
Included in the Prior Art Database: 2005-Aug-10
Document File: 3 page(s) / 427K

Publishing Venue

Siemens

Related People

Juergen Carstens: CONTACT

Abstract

Customary DIMMs (Dual In-line Memory Modules) using stacked components may have signal integrity problems on one of the chips or dies because a long flex is needed to connect the lower and the upper die (two stacks; four stacks at dual die version). This problem was seen on some busses DQ (Data), CA (Command Address), CTRL (Control) and CLK (clock) on all types of DIMMs (buffered DIMMs, registered DIMMs, unbuffered and SODIMMs). The situation got worse when the frequency of the bus (DQ, CA, etc.) was increased. Traditional package technology (Fig. 1) used the flex to connect upper die (2x stack) or upper dual die (4x stack) to the package balls. Bottom die or dual die was directly soldered on the balls. This produced a lot of load imbalance within the stacked package. Due to the asymmetry of the package and a very long stub length (flex), there was a big tendency of the bottom die (dual die) to so called eye collapse due to reflection.

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Multiple Substrate Packages

Idea: Siva Raghuram, DE-Munich; Srdjan Djordjevic, DE-Munich

Customary DIMMs (Dual In-line Memory Modules) using stacked components may have signal integrity problems on one of the chips or dies because a long flex is needed to connect the lower and the upper die (two stacks; four stacks at dual die version). This problem was seen on some busses DQ (Data), CA (Command Address), CTRL (Control) and CLK (clock) on all types of DIMMs (buffered DIMMs, registered DIMMs, unbuffered and SODIMMs). The situation got worse when the frequency of the bus (DQ, CA, etc.) was increased.

Traditional package technology (Fig. 1) used the flex to connect upper die (2x stack) or upper dual die (4x stack) to the package balls. Bottom die or dual die was directly soldered on the balls. This produced a lot of load imbalance within the stacked package. Due to the asymmetry of the package and a very long stub length (flex), there was a big tendency of the bottom die (dual die) to so called eye collapse due to reflection.

A solution of the problem is provided by implementing a multiple substrate package approach as shown in the examples in Fig. 2, 3 and 4. Now the stacking could be realized without a flex. Also RDLs (ReDistribution Layers) are not needed anymore. The most of routing is done within the substrate, and it is easier to control the impedance. The substrates are connected to each other using bond wires. The multiple substrate packages are much more symmetrical in comparison to the standard package shown in Fig. 1.

Using this solution, a good impedance matching of the package and also good timing within the system can be obtained.

Fig. 1: Stacked package with flex implemented (current technology)

FBGA

FBGA

flex

flex

adhesive

underfill

© SIEMENS AG 2005 file: ifx_2005J50923.doc page: 1

adhesive

underfill

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Fig. 2: Double substrate package (without f...