Abstract:
A stepped printed circuit board for a probe card and for clamping by a testing machine is disclosed. The stepped printed circuit board includes a main body and a protruding body. The main body has a conductive circuit pattern arranged therein and a border area for the clamping of the testing machine. The protruding body is joined to a bottom side of the main body beyond the border area and defines with the bottom side of the main body an elevational difference. The protruding body has a conductive circuit pattern arranged therein and electrically connected to the conductive circuit pattern of the main body.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to probe cards and more particularly, to a printed circuit board having a stepped structure for use in a probe card, and a probe card comprising the same. The present invention relates also to a method for clamping the probe card using the stepped printed circuit board. 
   2. Description of the Related Art 
   The function of an integrated circuit must be examined by means of a probe card before packaging, so that defective pieces can be removed, increasing the final yield rate. 
   A vertical probe card generally comprises a printed circuit board (hereinafter referred to ‘PCB’), an adapter substrate, and a probe head. The adapter substrate has one side joined to the PCB and electrically connected to the circuits of the PCB. The probe head is connected to the other side of the adapter substrate, allowing electric connection of the vertical probes of the probe head to the PCB. When in use, the PCB must be clamped by a testing machine to ensure stability of the probe card. However, the clamping size acceptable to the testing machine is limited. Therefore, the thickness of the PCB must be within the clamping size acceptable to the testing machine. Further, the adapter substrate is conventionally laminated layer by layer by the so-called built up process to increase its thickness. Because the thickness of each medium layer is limited to 30-60 μm and the adapter substrate has to be formed vias therein by laser ablation, the thickness of the adapter substrate is normally defined within 0.8-1.1 mm. The thickness limitation on the PCB and the adapter substrate and the length limitation on the vertical probes of the probe head may cause a contact failure between the vertical probes and the test sample after the testing machine has been adjusted to the bottom limit position. In this case, the test cannot be performed. 
   In order to eliminate the aforesaid problem, there are providers who join two PCBs or adapter substrates with solder balls by the reflow solder process, keeping the two PCBs or the adapter substrates electrically connected together. This method increases the total thickness of the probe card, however it also brings drawbacks. The first drawback is that the use of the solder balls to electrically connect the two PCBs or the adapter substrates causes a signal reflection and loss, resulting in a poor signal transmission quality. The second drawback is that the leveling between the two PCBs or the adapter substrates becomes poor after the reflow soldering process due to technical problem and manufacturing conditions, such as size difference of solder balls. The third drawback is that the bonding force of the solder balls after the reflow soldering process may vary with operating conditions, and the relatively thinner adapter substrate may be damaged or the solder balls may be forced out of place upon an impact. The fourth drawback is that the application of reflow soldering process relatively complicates the manufacturing process and increases the manufacturing cost. 
   SUMMARY OF THE INVENTION 
   The present invention has been accomplished under the circumstances in view. It is the main object of the present invention to provide a stepped PCB for use in a probe card, which increases the whole thickness of the probe card while fitting the specifications of regular testing machines, solving testing depth problem. 
   It is another object of the present invention to provide a stepped PCB for probe card, which prevents exposure of electric signal transmission line to the surroundings, thereby eliminating over-reflection and oxidation problems. 
   To achieve these objects of the present invention, a stepped printed circuit board provided by the present invention for a probe card and for clamping by a testing machine comprises a main body and a protruding body. The main body has a conductive circuit pattern arranged therein and a border area for the clamping of the testing machine. The protruding body is joined to a bottom side of the main body and defines with the bottom side of the main body an elevational difference. The protruding body has a conductive circuit pattern arranged therein and electrically connected to the conductive circuit pattern of the main body. 
   The present invention also provides a probe card comprises the aforesaid stepped printed circuit board and a probe head having a plurality of vertical probes electrically respectively connected to the protruding body. In an alternative example, the probe card comprises the aforesaid stepped printed circuit board, an adapter substrate electrically connected to the protruding body, and a probe head having a plurality of vertical probes electrically respectively connected to the adapter substrate. 
   In addition, the present invention also provide a method for clamping a probe card comprising the steps of (a) providing a probe card as defined above, (b) placing the probe card in a testing machine for enabling the border area of the main body to be clamped by the testing machine, and (c) electrically connecting the conductive circuit pattern of the main body to the testing machine. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic exploded view of a stepped PCB according to a first preferred embodiment of the present invention. 
       FIG. 2  is a schematic perspective assembly view of the stepped PCB according to the first preferred embodiment of the present invention. 
       FIG. 3  is a schematic sectional view, showing the stepped PCB according to the first preferred embodiment of the present invention in use with an adapter substrate and a probe head. 
       FIG. 4  is another schematic sectional view, showing the stepped PCB according to the first preferred embodiment of the present invention in use with a probe head. 
       FIG. 5  is a schematic perspective view of a stepped PCB according to a second preferred embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   As shown in  FIGS. 1-3 , a stepped PCB  100  in accordance with the first preferred embodiment of the present invention comprises a main body  10 , and a protruding body  20 . 
   The main body  10  is a PCB with a predetermined shape having a first side  11  and a second side  12  opposite to the first side  11 . The main body  10  can be made by laminating FR-4, FR-5, polyimide (PI) or BT materials through the built up process at a predetermined pressure and temperature. A conductive circuit pattern  13  is formed inside the main body  10  as shown in  FIG. 3  through the laminating process, and a plurality of conductive contacts  14  are respectively formed on the first side  11  and the second side  12  on the middle within a predetermined area and electrically connected to the circuit pattern  13 . The thickness of the main body  10  fits the clamping range of the conventional testing machine (about 3.2 mm-7.0 mm). The width of the main body  10  is within 6-17 inches. Therefore, the testing machine  50  can clamp the periphery of the main body  10 . 
   The protruding body  20  is a PCB having a predetermined shape. The size of the protruding body  20  is smaller than that of the main body  10 . The protruding body  20  has a top side  21  and a bottom side  21  opposite to the top side  21 . The protruding body  20  can be made by laminating FR-4, FR-5, polyimide (PI) or BT materials through the built up process at a predetermined pressure and temperature. A conductive circuit pattern  23  is formed inside the protruding body  20  as shown in  FIG. 3  through the laminating process, and a plurality of conductive contacts  24  are respectively formed on the top side  21  and the bottom side  22  on the middle within a predetermined area and electrically connected to the conductive circuit pattern  23 . The thickness of the protruding body  20  is about 0.5-6.0 mm. The width of the protruding body  20  is within 16 inches. 
   The above description describes the structure of the stepped PCB  100 . The installation and use of the stepped PCB  100  will be described hereinafter. 
   The configuration and location of the conductive contacts  24  at the top side  21  of the protruding body  20  are corresponding to the configuration and location of the conductive contacts  14  at the second side  12  of the main body  10 . Therefore, the conductive contacts  24  at the top side  21  of the protruding body  20  can be respectively bonded to the conductive contacts  14  at the second side  12  of the main body  10  by means of a laminating process using a polypropylene film that is common employed to the fabrication of PCBs, thereby joining the main body  10  and the protruding body  20  as a unity member. When the main body  10  and the protruding body  20  are joined together, the conductive circuit pattern  13  of the main body  10  and the conductive circuit pattern  23  of the protruding body  20  are electrically connected together. At this time, an elevation difference is produced between the second side  12  of the main body  10  and the periphery of the protruding body  20  due to the fact that the size of the protruding body  20  is smaller than that of the main body  10 , and the border area of the main body  10  corresponding to the area of the elevation difference is provided for clamping by the testing machine  50 . Further, an adapter substrate  30  is bonded with one side thereof to the bottom side  22  of the protruding body  20 , keeping the adapter substrate  30  electrically connected to the protruding body  20  and the main body  10 . The adapter substrate  30  has a predetermined configuration and is a known product, no further detailed description in this regard is necessary. Thereafter, a probe head  40  having a predetermined amount of vertical probes  41  is connected to the other side of the adapter substrate  30  opposite to the protruding body  20 , as shown in  FIG. 3 , enabling one end of each of the vertical probes  41  to be respectively and electrically connected to the adapter substrate  30  and the other end of each of the vertical probes  41  to be extended out of the adapter substrate  30  for the contact of the test sample, for example, an integrated circuit chip (not shown). At final, the connecting contacts  14  at the first side  11  of the main body  10  are respectively electrically connected to the testing machine  50 , enabling the tested signal to be transmitted from the test sample to the testing machine for processing. 
   According to the aforesaid design, the use of the protruding body  20  increases the total thickness of the PCB  100  while maintaining the clamping thickness that is provided by the main body  20  within a limited range acceptable to the testing machine  50 , i.e., the distance between the vertical probes  41  and the main body  10  at the testing machine  50  can be relatively increased, solving he problem of short test depth of the testing machine  50 . 
   Further, because the protruding body  20  and the main body  10  are bonded together through a laminating process at a high pressure and a high temperature as commonly employed to the fabrication of PCBs, no extra manufacturing process or cost will be produced. Further, because the conductive circuit pattern  13  and the conductive circuit pattern  23  are respectively formed inside the main body  10  and the protruding body  20 , i.e. they are not exposed to the outside, the invention eliminates signal reflection or loss. Further, the bonding of the protruding body  20  and the main body  10  is carried out by means of the use of a polished steel plate for positioning, the finished product has a better plainness. Further, because the protruding body  20  and the main body  10  are bonded together through a laminating process at a high temperature and a high pressure, the bonding strength is much higher than through a reflow soldering process. 
     FIG. 4  shows the stepped PCB  100  is cooperated with the probe head  40  only, i.e. the aforesaid adapter substrate  30 , is eliminated. Under this circumstance, the circuit of the aforesaid adapter substrate  30  is directly formed in the protruding body  20 , saving much component cost. 
     FIG. 5  shows a stepped PCB constructed according to the second preferred embodiment of the present invention. According to this embodiment, the stepped PCB, referenced by  200 , comprises a main body  60  and a protruding body  70 , which are integrally made. 
   In this embodiment, the thickness of the main body  60  is made greater than the clamping range of the testing machine when the main body  60  is originally made. Thereafter, the border area of the bottom side of the main body  60  is removed (by means of local etching or any PCB stripping method), and therefore the bottom center area of the main body  60  (the area that is beyond the testing machine clamping area) constitutes the protruding body  70 . This embodiment achieves the same effect as the aforesaid first preferred embodiment does.