> From:         A.J. Tufgar[SMTP:tufgaraj@MUSS.CIS.MCMASTER.CA]
> Sent:         Friday, May 14, 2004 4:45 PM
> To:   PICLIST@MITVMA.MIT.EDU
> Subject:      [EE]:  Problems with memory design.

> Hello all,
>          I'm haing a problem figuring out the best (cheapest) way to
> store 1024k x 8 (8Mb) of data for a battery powered data logging
> application.  The data doesn't have to be retained on power loss.

> I thought the best way to do this would be to use one of the following
> SRAM chips:
> http://www.cypress.com/cfuploads/img/products/CY62158CV33LL-70BAI.pdf

>http://www.samsung.com/Products/Semiconductor/SRAM/LowPower/LowPower_n_LowVoltage/8Mbit/K6X8008T2B/ds_k6x8008t2b.pdf

> The application is battery powered and suppose to be small so I don't
> care for the second chip much as it seems to be hard to find, very
> power hungry while operating and a larger package then the first.

> The first chip is excellent, however it's a FBGA and a very small one
> at that. So I'm really not sure how I can make a PCB for this with our
> standard board house 6mil space/6mil trace.  If I put vias under each
> pad the vias will be too big for the pins (my board house's smallest
> via is .35mm and the ball diameter is .3mm).  How is mounting of FPGAs
> typically done?  Can I put a pad under each outside pin then use vias
> in the middle and count on the solder paste on joining the balls to the
> vias?  Doesn't seem like a good idea, since the ball will not toush the
> via and I'm counting on the solder paste to bridge the gap when it
> melts.

> OR is there a cheaper way to store all my data than SRAM?

> Thnaks in Advance,
> Aaron

The Digi-Key catalog shows 8 Meg serial flash chips from Atmel. The
Atmel numbers  are AT45DB0818B-XX where XX is the package type.
The types are 28-TSOP (=TC, TI), 28 SOIC (=RC, RI), 14-CBGA
(=CC,CI), and 8-CASON (=CNC, CNI).  The 8 pin package type is not
familiar to me, but it seems small. Prices for the 8 pin type are
around $6. Supply voltage is 2.7V only.

Static RAM in  512k x 16 bit is available from ST Microelectronics,
also in the Digi-Key catalog. Just store words instead of bytes. The
package is 44-TSOP which might be tight but is easier than ball-
grid array. See Digi-Key P/N M68AW512ML70ND6.

John Power

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