I'm sure that many of us are anxious about how to choose a high quality memory module. Everybody is tired of the lottery of Mtec, NpNx and other similar companies when you never know whether you are buying a good or an out-of-order module. Taking into account a quite favorable present-day situation with prices of memory components, such modules will hardly interest many. The market today gives quite a wide choice among brand-name memory modules of excellent quality and of just good quality. The price plays a vital role here: not always these modules can be purchased at an acceptable sum of money. Besides, two other factors - efficiency and reliability are often alternative. But anyway, one can find solutions possessing harmonious combination of price, efficiency and reliability. One of such modules is Kingmax TinyBGA PC150.
In 1997 Kingmax already offered a TinyBGA case for packing DRAM dies, which was much similar to a µBGA and shared nearly all advantages of the latter over a standard TSOP. In 1998 Kingpak, a daughter company, registered a corresponding trade mark, and the mass production of SDRAM chips in TinyBGA cases started up. Today most SDR SDRAM chips produced by Kingmax are packed exactly in TinyBGA cases. And the KSV684T4A1A-06 chips mounted on our TinyBGA PC150 module are not an exclusion. Let's find out what advantages this type of case has as compared with other types.
Electrical parameters. First, TinyBGA cases allow reducing the length of signal ways (by 25-30 %, according to Kingmax engineers). It gives a possibility to reduce capacity, inductance and active resistance of the track "die - in-cut connection" which improves noise-immunity and frequency characteristics of the track. Another advantage over the TSOP case lies in the fact that TinyBGA pins have lower mutual capacitance and inductance. An amplitude of spurious signals induced in the neighbor flow lines is, therefore, getting smaller which, again, causes a better noise-immunity of the track.
It should be noted here that for reliable operation of memory modules it is vital to have a motherboard of high quality. Many factors depend on how good is the layout of the board and the shielding of signal lines of the track "chipset - in-cut connection", and whether electrical parameters of this track correspond to the specification requirements. Even the quality of the in-cut connection may cause problems if its transient resistance is too high. That is why one would hardly get good efficiency and an excellent speed of even the best memory module if it is installed in a fishy motherboard.
Compactness. The TinyBGA case is rather compact - 12X9X1.4 mm for 44-BALL TinyBGA and 13X11X1.4 mm for 54-BALL TinyBGA. Of course, the module itself is also small - 133.35X25.4X3.94 mm.
Temperature mode. According to Kingmax specialists, the TinyBGA case has a lower thermistor than the TSOP case. The die lies on a multilayer mount which has a good thermal contact with a printed circuit board. As a result, reduction of the Thetajb thermistor (junction-to-board) causes reduction of the overall thermistor - Thetaja (junction-to-ambient). The facilitated temperature mode gives not only a higher reliability but also better frequency characteristics.
All above-mentioned features relate to the TinyBGA case but not to the SDRAM die. As you can see, the case parameters are rather attractive (according to Kingmax engineers, TinyBGA can operate flawlessly even at 300 MHz). And how good the die is will be shown in the tests below.
Another interesting feature, I've forgotten to mention, is the support of not only two standard data transfer modes with a packet length equal to 2 and 4 bits (burst length = 2 and burst length = 4), but also of two additional modes - 8-bit packet (burst length = 8) and full page. The latter two modes are optional according to JEDEC standards on SDR SDRAM, and are not typical comparing to the majority of chips of other manufacturers. On the one hand, such support deserves praise, but on the other hand, these two modes are supported by far not all standard chipsets for PCs.
Kingmax TinyBGA PC150 module is delivered in a neat and cute retail-package. I think you would agree that a colorful retail-box makes much better impression than a polyethylene packet or a piece of foam-rubber tightened with elastic ;-)
As for the size, Kingmax's module is nearly 1.5 times lower than a standard PC133 module from Kingston.
The MPJA83S-683 module, we managed to put our hands on, is one-sided: there are only 8 chips on the printed circuit board, since only 128 Mbit SDRAM chips with 16MX8 organization (4M X 8 X 4 logic banks) are used. The printed circuit board and mounting of components give no cause for complaining. There is of course a flash memory chip 2 Kbit in size (2K EEPROM in an 8-pin SOP case) that realizes SPD mechanism (Serial Presence Detect). Besides, there are capacitive and resistance decouplings in feed and synchrosignal circuits for each chip.
The test system configuration:
Comment. The maximum clock speed of the bus ensuring a flawless system functioning is 156 MHz. At the frequencies up to 160 MHz errors were noticed in applications.
It is rather a good and well implemented module! Kingmax TinyBGA PC150 showed an exclusive efficiency at the standard frequency of 133 MHz with the most advanced timings: the performance increases greatly as compared with a standard 3-3-3 scheme. The module worked normally even at the frequency higher than 150 MHz (though, only with conservative timings). In view of the acceptable price, excellent performance and guaranteed reliability Kingmax's TinyBGA PC150 memory module can be recommended not only for overclockers but also for all PC users who are interested in a well-functioning memory subsystem.
Besides, it should be noted that all Kingmax TinyBGA
memory modules have a life-long warranty, well, that really must mean something !
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