Europaisches Patentamt (19) European Patent Office Office europeeneen des brevets ^ £ P 0 742 682 A2 (12) EUROPEAN PATENT APPLICATION (43) Date of publication: (51) Intel e H05K7/10 13.11.1996 Bulletin 1996/46 (21) Application number: 96302902.0 (22) Date of filing: 24.04.1996 (84) Designated Contracting States: (72) Inventors: DE FR GB IT • Hundt, Michael J. Double Oak, Texas 75067 (US) (30) Priority: 12.05.1995 US 440367 • Chiu, Anthony M. Richardson, Texas 75082 (US) (71) Applicant: SGS-THOMSON MICROELECTRONICS, INC. (74) Representative: Palmer, Roger et al Carrollton Texas 75006-5039 (US) PAGE, WHITE & FARRER 54 Doughty Street London WC1N2LS (GB) (54) Low-profile socketed integrated circuit packaging system (57) A socketed integrated circuit packaging sys- a hole therethrough to receive the conductive slug of the tem, including a packaged integrated circuit and a sock- integrated circuit package; the socket may also have its et therefor, is disclosed. The integrated circuit package own thermally conductive slug disposed within the hole includes a device circuit board to which a thermally con- of the frame. The socket has spring contact members ductive slug is mounted; the underside of the device cir- at locations matching the location of the lands on the cuit board has a plurality of lands arranged in an array. device circuit board. The integrated circuit package may The integrated circuit chip is mounted to the slug, be inserted into the socket frame, held there by a metal through a hole in the device circuit board, and is wire- or molded clip. A low profile, low cost, and high thermal bonded to the device circuit board and thus to the lands conductivity package and socket combination, is thus on the underside. The socket is a molded frame, having produced. Printed by Jouve, 75001 PARIS (FR) (Cont. next page) 1 EP 0 742 682 A2 2 Description the solder balls so that they will wet to lands on the circuit board, thus electrically and mechanically connecting the This invention is in the field of integrated circuits, component thereto. The solder reflow process is espe- and is more particularly directed to packages therefor. cially useful as it can be done at relatively low temper- Modern microprocessor-based data processing 5 atures, and the ability to surface-mount the BGA pack- systems, particularly personal computers and computer aged component eliminates the requirement of plated- workstations, are commonly upgradable in performance through holes in the system circuit board. In addition, and capability. Typically, this upgrading is performed by BGA packages allow a large number of terminals to oc- replacing the originally installed microprocessor that cupy a small board area, as the pitch of solder balls on serves as the central processing unit with a higher per- 10 the package can be quite small (e.g., on the order of 0.1 formance or more capable microprocessor. For exam- cm). The BGA package is also a very low profile pack- ple, one may upgrade a 386-based personal computer age, and is thus especially suitable for small systems by removing the originally installed 386-type microproc- such as notebook-size personal computers and the like. essor and inserting, in its place, a 486-type microproc- However, according to the current state of the art, essor; by way of further example, one may upgrade the is the benefits of BGA packages are not available if the central processing unit by replacing the originally in- component is to be installed by way of a socket. Firstly, stalled microprocessor with a microprocessor of the the low profile provided by the BGA package is lost, for same type (e.g., 486-type) that can operate at a faster the most part, when the height of the socket is to be clock rate. Of course, other simple and minor adjust- added to the system. Secondly, the solder balls tend to ments of certain settings in the computer may also need 20 provide poor performance as a mechanical connection to be made to accommodate the upgraded central (i.e., when not reflowed to provide a solder connection). processing unit. This is because conventional solder compositions tend Therefore, in the manufacture of upgradable per- to migrate, or creep, under mechanical force. In addi- sonal computers, certain integrated circuits (e.g., at tion, the mechanical force required to make electrical least the microprocessor) are installed into the system 25 contact to a cold solder ball is quite high (e.g., on the circuit board by way of sockets, rather than by being sol- order of one ounce), exacerbating the problem of solder dered directly to the circuit board, to facilitate removal creep under mechanical stress. This high contact force and reinstallation of these components. Conventional is required in order to overcome the native oxide that sockets include sockets of the type that apply a mechan- rapidly forms over the surface of conventional solder ical force to pins of the integrated circuits so as to make 30 balls. Despite these barriers, sockets for making remov- contact thereto. However, as the number of terminals able connection to solder balls on a BGA package are for microprocessors increase to more than 150 termi- known in the art, as will now be described relative to nals, the total friction encountered in removing the mi- certain examples. croprocessor from such sockets becomes substantial, Figures 1 a and 1 b illustrate a first example of a con- and may require a removal force of such magnitude as 35 ventional socket for BGA components, such as is avail- to crack or otherwise damage the board. While zero-in- able from Methode Electronics, Inc. In this example, re- sertion force sockets are also well known in the art, ferring to Figure 1 a, BGA package 2 is converted into a these sockets are generally quite expensive. pin-grid-array package (PGA), by reflow soldering of the In addition, it is of course desirable to manufacture BGA package 2 to pin board 4. As shown in the cross- circuit boards with low-profile components, so that the 40 section of Figure 1b, pin board 4 solder connects each overall height of the circuit board and its components is solder ball 3 of BGA package 2 to a corresponding pin relatively low. This allows for the size of the overall sys- 5 extending through pin board 4. The combination of tem to be quite small, which is especially important for BGA package 2 and pin board 4, so assembled, acts as portable personal computers, such as those of the pop- a PGA package, and may now be inserted into conven- ular notebook size. However, conventional sockets, es tional socket 6 that is soldered to the surface of system such as those described above, significantly raise the circuit board 8. As shown in detail in Figure 1b, each of height of the circuit board and its components. The sys- pins 5 of pin board 4 extend into and are received by pin tem designer and user are thus faced with the choice sockets 7 in socket 6. Pin sockets 7 are each soldered between reduced system size and upgradability in these to system circuit board 8, by way of solder joints 9 as circumstances. so shown in Figure 1b. However, as is evident from Figure By way of further background, ball-grid array (BGA) 1 b, the presence of both socket 6 and pin board 4, along packages have become popular in the art, particularly with the height of reflowed solder balls 3, result in a rel- for packaging microprocessors. As is well known, the atively high profile combination package system. Fur- terminals of a BGA package are solder balls, formed on thermore, the cost of this package system can be quite the underside of the package and attached to plated 55 high, considering that two additional piece parts (pin lands thereat. A solder reflow process is then used to board 4 and socket 6) are required. attach the BGA component to a circuit board after its Referring now to Figures 2a and 2b, another exam- placement thereat; the heat of the reflow process melts ple of a conventional socketing arrangement for a BGA 3 3 EP 0 742 682 A2 4 package, manufactured and sold by AMP, will now be cated over the chip and bond locations on the device described for purposes of further background. As shown circuit board, for environmental protection. The under- in Figure 2b in cross-section, BGA package 12 has sol- side of the device circuit board surrounding the thermal- der balls 1 3 connected thereto, extending from the bot- ly conductive slug has a plurality of plated lands, each tom surface thereof. Solder balls 1 3 are received by re- 5 connected to the integrated circuit chip therewith. The ceptacles 16 in socket 14, which in turn is soldered to socket is formed of molded plastic, and has an arrange- system circuit board 18 by way of solder joints 19. Re- ment of spring elements extending therethrough that are ferring to the plan view of Figure 2b, receptacles 1 6 are, arranged to correspond to the plated lands on the un- in this example, configured as partially split rings, so that derside of the device circuit board. Surface mounting burrs 17 are present on the inner diameter of recepta- 10 technology is used to solder the socket to the system cles 1 6. Burrs 1 7 serve to cut into solder balls 1 3 when circuit board, allowing the land-grid-array package to be BGA package 12 is installed over socket 14, and thus inserted and removed from the socket without soldering.