Memory-module board layout for use with memory chips of different data widths

A memory module comprising:

• a circuit board having a size for fitting into a memory module socket on a motherboard;
• a plurality of memory chips including a front-side memory chip mounted on a front side of the circuit board and a back-side memory chip mounted to a back side of the circuit board;
• the memory chips having a first data width when a first type of memory module is manufactured from the circuit board, and having a second data width when a second type of memory module is manufactured from the circuit board;
• wherein the second data width contains more data bits that the first data width;
• a connector along a bottom edge of the circuit board, the connector for making electrical connection with data signals on the motherboard, the connector mating with the memory module socket when inserted;
• a plurality of paired footprints, each for driving a different data group of the data signals through the connector;
• a front-side location, in a paired footprint, having mounted thereon the front-side memory chip;
• front-side solder pads in the front-side location, soldered to leads of the front-side memory chip;
• a first front-side pad group of the front-side solder pads that are soldered to a first front-side lead group of data-carrying leads to the front-side memory chip;
• a second front-side pad group of the front-side solder pads that are soldered to a second front-side lead group, the second front-side lead group being data-carrying leads to the front-side memory chip when the memory chips are of the second data width;
• wherein the second front-side lead group comprises dummy leads that do not carry data to the front-side memory chip when the memory chips are of the first data width;
• a front-side chip-select input to the front-side memory chip, the front-side chip-select input selecting the front-side memory chip for data access;
• a back-side location, in the paired footprint, having mounted thereon the back-side memory chip;
• back-side solder pads in the back-side location, soldered to leads of the back-side memory chip;
• a first back-side pad group of the back-side solder pads that are soldered to a first back-side lead group of data-carrying leads to the back-side memory chip;
• a second back-side pad group of the back-side solder pads that are soldered to a second back-side lead group, the second back-side lead group being data-carrying leads to the back-side memory chip when the memory chips are of the second data width;
• wherein the second back-side lead group comprises dummy leads that do not carry data to the back-side memory chip when the memory chips are of the first data width;
• a back-side chip-select input to the back-side memory chip, the back-side chip-select input selecting the back-side memory chip for data access;
• first wiring traces on the circuit board that connect the first front-side pad group to a first set of data signals in a data group for the paired footprint and connect the first back-side pad group to a second set of data signals in the data group for the paired footprint, the first set and the second set being non-overlapping sets of data signals;
• second direct wiring traces on the circuit board that connect the second front-side pad group to the second set of data signals in the data group for the paired footprint;
• and
• second cross-over wiring traces on the circuit board that connect the second back-side pad group to the first set of data signals in the data group for the paired footprint,
• whereby the circuit board supports manufacture using memory chips of the first data width and of the second data width.

A multi-type memory module board comprising:

• substrate board means for supporting memory chips and wiring traces,
• edge connector means for mating with metal connectors in a memory module socket on a motherboard, the edge connector means including data lines;
• a plurality of layout pairings on the substrate board means that each drive different data groups of data lines in the edge connector means, each layout pairing comprising:
• first multi-type footprint means, on a front side of the substrate board means, for accepting a first memory chip;
• wherein the first memory chip has a first data width when a first type of memory module is being assembled from the multi-type memory module board, and has a second data width when a second type of memory module is being assembled from the multi-type memory module board;
• wherein the second data width is larger than the first data width;
• first solder pad means, surrounding the first multi-type footprint means, for forming solder connections to metal leads of the first memory chip during assembly;
• first wiring means, formed on or within the substrate board means, for connecting a first data group of the first solder pad means to a first data group of the data lines in the edge connector means;
• second wiring means, formed on or within the substrate board means, for connecting a second data group of the first solder pad means to a second data group of the data lines in the edge connector means;
• second multi-type footprint means, on a back side of the substrate board means, for accepting a second memory chip;
• second solder pad means, surrounding the second multi-type footprint means, for forming solder connections to metal leads of the second memory chip during assembly;
• first cross-over wiring means, formed on or within the substrate board means, the first cross-over wiring traces connecting a first data group of the second solder pad means to the second data group of the edge connector means;
• and
• second cross-over wiring means, formed on or within the substrate board means, for connecting a second data group of the second solder pad means to the first data group of the edge connector means;
• wherein when the first and second memory chips each have the first data width, the first memory chip drives data onto the first data group in the edge connector means but does not drive data onto the second data group in the edge connector means, and the second memory chip drives data onto the second data group in the edge connector means but does not drive data onto the first data group of in the edge connector means;
• wherein when the first and second memory chips each have the second data width, the first memory chip drives data onto the first data group in the edge connector means and drives data onto the second data group of in the edge connector means in response to a first chip-select signal, and the second memory chip drives data onto the first data group in the edge connector means and drives data onto the second data group of in the edge connector means in response to a second chip-select signal;
• wherein the first and second chip-select signals are activated on different access cycles for memory chips having the second data width,
• whereby the multi-type memory module board is assembled into the first type of memory module when the first and second memory chips have the first data width, and into the second type of memory module when the first and second memory chips have the second data width.