NEW TAB OUTER LEAD ASSEMBLY METHOD- TAB PAD GRID ARRAY CARRIER (01-Dec-1992)

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MOlOROLA INC. Technical Developments Volume 17 December 1992

NEW TAB OUTER LEAD ASSEMBLY METHOD-

TAB PAD GRID ARRAY CARRIER

by Harry Geyer

   The TAB Grid Array is a combination of TAB ILB and a pad grid array for the OLB. The inner leads make contact to the die and then fan out to a matrix of solder halls. The tape has two metal layers, one consists of the signal leads from the die to the outer lead area and the other consists of copper pads for the solder balls with thru holes to the signal layer. The tape is then laminated to a thin PCB. Aher the lamination step, solder balls are attached to the copper pads. The solder balls can have a pitch from .040" to .lOO!' A heat sink may be attached to the die and to the top of the PCB to increase the power dissipation of the package.

  A major diKerence between conventional TAB and the TAB Pad Array carrier is the method of assembling the device on the board. TAB assembly requires a machine, an OLB bonder, which shears and bends the leads, excises and transfers the TAB component to the PCB, and bonds the component to the PCB using a hot bar thermode. In addition the OLB process also requires very precise screening of the solder paste or solder plated boards. The special solder process is required to accom- modate the very fine pitch of the OLB leads, which vary hehveen 4 mils. (for direct chip attach) to 20 mils. See Figure 1 which shows a typical TAB device mounted in a tape carrier. Figure 2 shows a TAB device mounted to a PC. board using a OLB bonder. The TAB Pad Array carrier uses the same assembly processes used to assem- ble surface mount packages. The conventional solder

pads, pick and place equipment, and the solder reflow processes are applicable.

  There are some manufacturers who would like to use TAB for high lead count die but...