Thin memory module.

0001The present invention relates to a thin-type single in-line memory module (SIMM), especially to that used in a work station, personal computer, or the like.

0002Conventional work stations and personal computers as hardware have a structure in which a plurality of sockets, to which SIMMs are set, are provided on a substrate (to be called mother board hereinafter). Figs. 1 to 3 are examples of the sockets to which SIMMs are set, more specifically, 30 pin type SIMM module sockets (Pitch P = 2.54 mm, two-row straight type). Fig. 1 shows a one-side type socket; Fig. 2 shows a both-side type; and Fig. 3 shows a low-profile type.

0003Figs. 4 and 5 each show a structure of an SIMM. Fig. 4 is a one-side type SIMM, and Fig. 5 is a both-side type. As shown in these figures, chip condensers and memory ICs 2 are mounted on the surface of a print substrate 1. When memory ICs and other elements are arranged on the surface of the print substrate 1, the size of the mother board can be made smaller, as compared to the case where the memory ICs and others are mounted directly on the mother board. Thus, high density mounting of memory ICs and other elements on a board can be achieved.

0004However, the pitch of the sockets provided on the mother board is determined by the thickness of each of the SIMMs, and the interval between each adjacent pair of SIMMs. Generally, the intervals between each adjacent pair of SIMMs are 7.62 mm (average) for those of the one side type, 10.16 mm (average) for those of the both side type, and 12.7 mm (average) for those of the low profile type. The thickness A of an SIMM, as shown in Fig. 4, is determined by the thickness of the print substrate 1, and the thickness of the packages of the memory ICs 2. As a package of the memory IC 2, a small outline J lead package (to be called SOJ hereinafter), or a small outline package (to be called SOP hereinafter), and the like are generally used.

0005Although an increase in integration density of a mother board is somehow possible by reducing its socket pitch, the thickness of the above-mentioned SOJ or SOP is the main determinant of the socket pitch in conventional techniques. In connection with this, it is very difficult with such techniques to increase the integration density of a mother board.

0006It should be noted here that there are SIMMs of a type to which leads 3 are fixed onto a print substrate 1 itself so that the print substrate is directly set to a via-hole, as shown in Fig. 6. However, it is still very difficult, with this type also, to arrange memory ICs and the like at a high density due to the thicknesses of the SOJ and SOP mounted on the print substrate 1.

0007The present invention has been proposed to solve the above-mentioned problems, and the purpose thereof is to increase integration of memory ICs and other elements in an arrangement, and decrease the size of the system as a whole, by reducing the socket pitch.

0008To achieve the above purpose, the thin-type memory module according to the present invention comprises a substrate to be set to a socket provided on a mother board, and semiconductor devices each made of a thin-type package, mounted on one of or both surfaces of said substrate.

0009Further, the thin-type memory module according to the present invention comprises a substrate to be inserted to a socket provided on a mother board, and semiconductor devices each made of a thin-type small outline package, mounted on one of or both surfaces of said substrate.

0010This invention can be more fully understood from the following detailed description when taken in conjunction with the accompanying drawings, in which: <ul id="ul0001" list-style="none"><li>Figs. 1 to 3 show conventional sockets;</li><li>Figs. 4 to 6 show conventional SIMMs; and</li><li>Figs. 7 to 9 show side views of examples of the sockets to which thin-type memory modules of the present invention are set.</li></ul>

0011An embodiment of the present invention will now be described with reference to accompanying drawings.

0012The SIMM of the present invention has a structure in which thin-type packages, such as thin-type package small outline packages (TSOP), are mounted onto one of or both sides of a print substrate. The definition of a thin-type package is that of the total thickness of the stand-off of the package and the mold resin is no more than 1.2 mm. When thin-type package are used, the thickness of an SIMM onto which such packages are mounted can be made less than the conventional ones, and therefore the socket pitch thereof can be reduced. Accordingly, an increase in integration of arrangement of substrates can be achieved, and the size of the system can be decreased.

0013Fig. 7 shows eight one-side mount sockets provided on a mother board. An SIMM on which thin-type packages are set is engaged with each of these sockets. According to this structure, the following effect can be obtained.

0014Assume that eight one-side mounting sockets are provided on a mother board, and conventional SIMMs of a type by which two sockets are regarded as a pair, are used. In this case, the width H of a socket pair is 14.99 mm (average), and therefore a mount space S for mounting the eight one-side mount sockets is given by: <maths id="math0001" num=""><math display="inline"><mrow><mtext>S = 4 × H = 59.96 mm   (1)</mtext></mrow></math><img file="EP0476685A2_D0001.tif" /></maths>

0015Further, as is shown in Fig. 1, the thickness A₁ of a one-side mount type SIMM to which 1MDRAMs are set 4.97 mm (average); therefore when the pitch P of a socket is 7.62 mm, the distance D₁ between adjacent pair of SIMMs is given by: <maths id="math0002" num=""><math display="inline"><mrow><mtext>D₁ = P - A₂ = 2.45 mm   (2)</mtext></mrow></math><img file="EP0476685A2_D0002.tif" /></maths>

0016As can be seen also in Fig. 1, the thickness A₂ of a one-side mount type SIMM to which 4MDRAMs are mounted is 5.17 mm (average); therefore when the pitch P of a socket is 7.62 mm, the distance D₂ between adjacent pair of SIMMs is given by: <maths id="math0003" num=""><math display="inline"><mrow><mtext>D₂ = P - A₂ = 2.45 mm   (3)</mtext></mrow></math><img file="EP0476685A2_D0003.tif" /></maths>

0017Thus, the average distance D of adjacent pair of SIMMs is, from equations (2) and (3), given by: <maths id="math0004" num=""><math display="inline"><mrow><mtext>D = (D₁ + D₂)/2 = 2.55 mm   (4)</mtext></mrow></math><img file="EP0476685A2_D0004.tif" /></maths>

0018In the meantime, as is shown in Table 1 below, the thickness A₃ of a one-side mount type SIMM to which TSOPs are set is 2.77 mm (average). Therefore, when the pitch P of a socket is 7.62 mm, the distance D₃ of adjacent pair of SIMMs is given by: <maths id="math0005" num=""><math display="inline"><mrow><mtext>D₃ = P - A₃ = 4.85 mm   (5)</mtext></mrow></math><img file="EP0476685A2_D0005.tif" /></maths>

0019Further, if the distance between adjacent pair of SIMMs is set to the above-obtained average distance D, the number of SIMMs which can be arranged in the above mount space S is given by: <maths id="math0006" num=""><math display="inline"><mrow><mtext>A3·X + D(X-1) = S</mtext></mrow></math><img file="EP0476685A2_D0006.tif" /></maths>

0020Therefore, X = 12 In other words, when SIMMs to which TSOPs are set are employed, the mounting density can be increased by about 1.5 times as much in the same area as that of the conventional ones. <tables id="tabl0001" num="0001"><table frame="all"><title>Table 1</title><tgroup cols="2" colsep="1" rowsep="1"><colspec colnum="1" colname="col1" colwidth="78.75mm" /><colspec colnum="2" colname="col2" colwidth="78.75mm" /><thead valign="top"><row><entry namest="col1" nameend="col1" align="center">Package Loaded in Substrate</entry><entry namest="col2" nameend="col2" align="center">Thickness of SIMM (mm)</entry></row></thead><tbody valign="top"><row><entry namest="col1" nameend="col1" align="right">1M DRAM</entry><entry namest="col2" nameend="col2" align="char" char=".">4.97</entry></row><row><entry namest="col1" nameend="col1" align="right">4M DRAM</entry><entry namest="col2" nameend="col2" align="char" char=".">5.17</entry></row><row rowsep="1"><entry namest="col1" nameend="col1" align="right">TSOP</entry><entry namest="col2" nameend="col2" align="char" char=".">2.17</entry></row></tbody></tgroup></table></tables>

0021Fig. 8 shows eight both-side mount sockets provided on a mother board. An SIMM to which thin-type packages are set is engaged with each of these sockets. According to this structure, the following effect can be obtained.

0022Assume that eight both-side mount sockets are provided on a mother board, and conversional SIMMs are used. In this case, the mount space S for the eight one-side mounting sockets is: <maths id="math0007" num=""><math display="inline"><mrow><mtext>S = 78.49 mm   (6)</mtext></mrow></math><img file="EP0476685A2_D0007.tif" /></maths>

0023Further, as is shown in Fig. 2, the thickness A₁ of a both-side mount type SIMM on which 1MDRAMs are mounted is 8.67 mm (average); therefore when the pitch P of the socket is 10.16 mm, the distance D₁ between adjacent pair of SIMMs is given by: <maths id="math0008" num=""><math display="inline"><mrow><mtext>D₁ = P - A₂ = 1.49 mm   (7)</mtext></mrow></math><img file="EP0476685A2_D0008.tif" /></maths>

0024As can be seen also in Fig. 1, the thickness A₂ of a both-side mount type SIMM to which 4MDRAM are set is 9.07 mm (average); therefore when the pitch P of the sockets is 10.16 mm, the distance D₂ between adjacent pair of SIMMs is given by: <maths id="math0009" num=""><math display="inline"><mrow><mtext>D₂ = P - A₂ = 1.09 mm   (8)</mtext></mrow></math><img file="EP0476685A2_D0009.tif" /></maths>

0025Thus, the average distance D of adjacent pair of SIMMs is, from equations (2) and (3), given by: <maths id="math0010" num=""><math display="inline"><mrow><mtext>D = (D₁ + D₂)/2 = 1.29 mm   (9)</mtext></mrow></math><img file="EP0476685A2_D0010.tif" /></maths>

0026In the meantime, the thickness A₃ of a both-side mount type SIMM to which TSOPs are set is 4.27 mm (average). Therefore, when the pitch P of the sockets is 10.16 mm, the distance D₃ between adjacent pair of SIMMs is given by: <maths id="math0011" num=""><math display="inline"><mrow><mtext>D₃ = P - A₃ = 5.89 mm   (10)</mtext></mrow></math><img file="EP0476685A2_D0011.tif" /></maths>

0027Further, if the distance of adjacent pair of SIMMs is set to the above-obtained average distance D, the number of SIMMs which can be arranged in the above mount space S is given by: <maths id="math0012" num=""><math display="inline"><mrow><mtext>A₃·X + D(X-1) = S</mtext></mrow></math><img file="EP0476685A2_D0012.tif" /></maths>

0028Therefore, X = 14 In other words, when SIMMs on which TSOPs are mounted are employed, the mounting integration can be increased by about 1.75 times as much in the same area as that of the conventional one. <tables id="tabl0002" num="0002"><table frame="all"><title>Table 2</title><tgroup cols="2" colsep="1" rowsep="1"><colspec colnum="1" colname="col1" colwidth="78.75mm" /><colspec colnum="2" colname="col2" colwidth="78.75mm" /><thead valign="top"><row><entry namest="col1" nameend="col1" align="center">Package Loaded in Substrate</entry><entry namest="col2" nameend="col2" align="center">Thickness of SIMM (mm)</entry></row></thead><tbody valign="top"><row><entry namest="col1" nameend="col1" align="right">1M DRAM</entry><entry namest="col2" nameend="col2" align="char" char=".">8.67</entry></row><row><entry namest="col1" nameend="col1" align="right">4M DRAM</entry><entry namest="col2" nameend="col2" align="char" char=".">9.07</entry></row><row rowsep="1"><entry namest="col1" nameend="col1" align="right">TSOP</entry><entry namest="col2" nameend="col2" align="char" char=".">4.27</entry></row></tbody></tgroup></table></tables>

0029Fig. 9 shows eight both-side mount sockets provided onto a mother board. According to this structure, if SIMMs to which TSOPs are set are employed, the mounting integration can be significantly increased.

0030Needles to say, the present invention can be applied to SIMMs having a structure shown in Fig. 6.