Abstract:
A test head for a semiconductor integrated circuit tester includes first and second card cages and first and second groups of interface connectors for engagement by DUT edges of pin electronics cards installed in the first and second card cages respectively. The interface connectors of the first group are inclined at an angle less than 180° to the interface connectors of the second group.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   Subject matter disclosed in this application may be considered to be related to subject matter disclosed in copending patent application Ser. No. 10/877,478 filed Jun. 25, 2004, the entire disclosure of which is hereby incorporated by reference herein for all purposes. 
   BACKGROUND OF THE INVENTION 
   This invention relates to a test head for an integrated circuit tester. 
   The test head of a conventional semiconductor integrated circuit tester may be used in conjunction with a wafer prober. The test head is typically placed directly above the wafer prober for sequentially testing wafers that are delivered to the test head from below. The test head houses pin electronics on rectangular pin electronics cards, and the pin electronics cards are disposed in the test head so that each card lies in a vertical plane with vertical and horizontal edges. Each card has pin electronics terminals distributed along its lower horizontal edge and these terminals are connected to the device under test (DUT) through a so-called pogo tower, a DUT board (or device interface board) and a probe card. 
   In operation of the test head, a large amount of heat is dissipated from the pin electronics. Heat is removed from the test head by inducing a flow of air over the surfaces of the pin electronics cards. The pin electronics cards may be arranged so that they radiate from a vertical axis, but heat removal is more efficient if the cards are disposed parallel to each other. For compactness, the cards may be arranged in two parallel rows. 
   It is desirable that the signal path length between a pin electronics terminal of a pin electronics card and the corresponding terminal of the probe card should be short and should be uniform over all the pin electronics terminals. 
   The distance between a pin electronics terminal of a pin electronics card and the corresponding terminal of the probe card depends on the position of the pin electronics terminal along the lower edge of the pin electronics card. In order to achieve the desired uniform signal path length, it is necessary to compensate for the variation in distance between the pin electronics terminals of the pin electronics cards and the corresponding terminals of the probe card. This can be accomplished by appropriately designing the pattern of conductive traces of the DUT board, but the DUT board is then more expensive than would otherwise be the case. 
   To increase heat removal efficiency, it would be desirable to provide an air collection plenum between the two rows of pin electronics cards, but this would increase the distance between the pin electronics terminals and the corresponding terminals of the probe card, exacerbating the problem of non-uniformity of signal path length. 
   SUMMARY OF THE INVENTION 
   In accordance with a first aspect of the invention there is provided a test head for a semiconductor integrated circuit tester, the test head comprising first and second card cages, and first and second groups of interface connectors for engagement by DUT edges of pin electronics cards installed in the first and second card cages respectively, and wherein the interface connectors of the first group are inclined at an angle less than 180° to the interface connectors of the second group. 
   In accordance with a second aspect of the invention there is provided a test head for an integrated circuit tester, the test head comprising first and second card cages, and first and second groups of pin electronics cards located in the first and second card cages respectively, each pin electronics card having a DUT edge and an opposite tester edge, and wherein the DUT edges of the first group of pin electronics cards are inclined at an angle less than 180° to the DUT edges of the second group of pin electronics cards. 
   In accordance with a third aspect of the invention there is provided a test head for an integrated circuit tester, the test head comprising first and second card cages, each card cage having first and second opposite walls, wherein the first and second walls of the first cage are parallel to each other, the first and second walls of the second cage are parallel to each other, the first and second walls of each card cage are formed with guides for receiving pin electronics cards, the first wall of the first card cage is nearer than the second wall of the first card cage to the second card cage, the first wall of the second card cage is nearer than the second wall of the second card cage to the first card cage, and the first wall of the first card cage and the first wall of the second card cage are mutually inclined at an acute angle. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a better understanding of the invention, and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which 
       FIG. 1  is an end view of a test head of a semiconductor integrated circuit tester, and 
       FIG. 2  is a partially broken away top plan view of the test head shown in  FIG. 1 . 
   

   DETAILED DESCRIPTION 
   The test head illustrated in the drawings comprises an inner main housing having two vertical end walls  10 ,  14  and two outer side walls  18 ,  22  that are perpendicular to the end walls. The main housing has two interior walls  26 ,  30  that are in spaced, parallel relationship with the side walls  18 ,  22  respectively. The two pairs of walls  18 ,  26  and  22 ,  30  define respective compartments. Each of the walls  18 ,  22 ,  26 ,  30  is provided with guides (not shown) that define slots for receiving up to eighteen rectangular pin electronics cards  34 . Thus, each pair of walls provides a card cage for up to eighteen cards. The slots are arranged so that each pin electronics card is disposed in a vertical plane and the cards are parallel to each other. At the base of each slot is an interface connector  36  that is engaged by the pin electronics card when it is installed in the slot. Each card has a releasable retention latch (not shown) for holding the card in position when it has been installed. Each card is provided at its upper edge with a receptacle  38  of a multi-pin connector. The test head is used in conjunction with a server for supplying test instructions to, and receiving test data from, the pin electronics cards. 
   It will be seen from  FIG. 1  that the side walls  18 ,  22  and interior walls  26 ,  30  of the compartments are not vertical but, on the contrary, are inclined to the vertical such that the interior walls  26 ,  30  converge downwardly and define a V-shaped chamber therebetween. The chamber is closed at the top by a fan support plate  40 , and two rows of three fans  42  are mounted in the fan support plate. 
   In normal operation, the chamber is at the suction side of the fans and the fans induce a flow of cooling air through the perforated side walls  18 ,  22  and interior walls  26 ,  30 , as shown by the dashed lines and arrows, into the V-shaped chamber which therefore serves as an air collection plenum between the two interior walls  26 ,  30 . The cooling air flows between the pin electronics cards, removing heat from the pin electronics. The fans discharge air upwardly from the chamber. Because the interior walls  26 ,  30  diverge upwardly, an adequate plenum is provided even though the minimum distance between the interior walls  26 ,  30  is quite small. 
   The bottom walls of the two compartments converge upwardly at an angle α of about 135° and the interface connectors  36  are accordingly inclined to the horizontal at an angle of about 22.5°. For a given volume of the plenum, the lower edges of the interior walls  26  and  30  are closer together than if the walls  26  and  30  were parallel. Further, because the bottom walls of the compartments converge upwards, the proximal ends  36 P of the interface connectors are closer together than if the bottom walls were horizontal, for a given volume of the plenum. 
   As shown in  FIG. 1 , the test head is positioned above a wafer prober (shown partially and only schematically) that is used to deliver wafers to the test head from below. The pin electronics cards are electrically connected to the device under test through the interface connectors  36 , a pogo tower, a DUT board  44 , a pogo tower  46 , and a probe card  48 . The pattern of conductive traces on the DUT board is designed so that variations in signal path length between the pin electronics terminals and the corresponding terminals of the probe card are within an acceptable limit. Because the proximal ends  36 P of the interface connectors on the two sides of the test head are relatively close together, and the distal ends  36 D are relatively close together and are closer than the proximal ends  36 P to the DUT board, less space is required on the DUT board for conductor traces that would otherwise be needed to compensate for variation in signal path length. 
   The housing includes two covers  56  that pivot relative to the housing walls for engaging and disengaging the connectors  38  at the upper edges of the pin electronics cards  34 . The pivot axes of the two covers (only one of the pivot axes, designated  52 , is shown in  FIG. 1 ) are perpendicular to the planes of the pin electronics cards and are disposed over the air collection plenum. Each cover incorporates a backplane  56  that includes connectors  60  for supplying power and signals to the pin electronics cards, and for receiving signals from the pin electronics cards. The connectors  60  are in turn connected to cables  62  that enter the cover at the hinge edge  64  of the cover. 
   When the test head is in use, it is located in an outer casing  68  that conforms generally in configuration to the exterior configuration of the main housing and has two downwardly converging side walls  70  and two upwardly converging top walls  72  (one of which is shown separately from the rest of the casing) that meet above the plenum. The casing also has two opposite end walls  74  ( FIG. 2 ) and at least one of the end walls is formed with an opening for permitting entry of cables and hoses. The casing has two air inlet ports  76  in the side walls and two rows of three air outlet ports  78  in the top walls respectively. 
   A fan duct  82  is positioned above the plenum. The fan duct is a thermoformed structure that is located between the test head housing and the outer casing  68  and provides two rows of air ducts  84  that extend from the pressure side of the fans to the air outlet ports  78  of the outer casing. 
   Cables and hoses are threaded between the two rows of ducts and are branched off to each side, between the ducts in each row, for connection to the backplanes  56 . 
   Because the cables and hoses enter the cover at the hinge edge and the cover moves pivotally for engaging and disengaging the pin electronics cards, potential damage to the cables and holes during engaging and disengaging movement of the cover is avoided without it being necessary to provide substantial slack in the cables. 
   It will be appreciated that the invention is not restricted to the particular embodiment that has been described, and that variations may be made therein without departing from the scope of the invention as defined in the appended claims and equivalents thereof. For example, the invention is not restricted to the bottom walls of the two compartments converging at an angle of about 135°. It is desirable that the bottom walls converge at an angle in the range from 60° to 175°, and it is preferred that the angle be at least 120°. Unless the context indicates otherwise, a reference in a claim to the number of instances of an element, be it a reference to one instance or more than one instance, requires at least the stated number of instances of the element but is not intended to exclude from the scope of the claim a structure or method having more instances of that element than stated.