Dismiss
InnovationQ will be updated on Sunday, Oct. 22, from 10am ET - noon. You may experience brief service interruptions during that time.
Browse Prior Art Database

PCB BASED QFP WITH AREA ARRAY TEST CONTACTS- A TRANSITIONAL PACKAGE FROM QFPS TO BGAS

IP.com Disclosure Number: IPCOM000007268D
Original Publication Date: 1994-Oct-01
Included in the Prior Art Database: 2002-Mar-08
Document File: 4 page(s) / 178K

Publishing Venue

Motorola

Related People

John Baird: AUTHOR [+4]

Abstract

A new package design methodology for high pincount printed circuit board based QFP packages has been developed which has two unique benefits. First, this PCB design enables a low risk customer package conversion from a peripheral leaded QFP to an area array BGA, using the identical board design. Second, this design concept enables the use of an alternate electrical test method for PCB based QFP packages by making electrical contact through the robust BGA pads instead ofthe QFP leads.

This text was extracted from a PDF file.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 49% of the total text.

Page 1 of 4

0 M

MOIY)ROLA Technical Developments Volume 23 October 1994

PCB BASED QFP WITH AREA ARRAY TEST CONTACTS-

A TRANSITIONAL PACKAGE FROM QFPS TO BGAS

by John Baird, Denise Ommen, Tim Jones and John Bramwell

THE DESIGN METHODOLOGY

DESIGN METHODOLOGY APPLICATION

  A new package design methodology for high pincount printed circuit board based QFP packages has been developed which has two unique benefits. First, this PCB design enables a low risk customer package conversion from a peripheral leaded QFP to an area array BGA, using the identical board design. Second, this design concept enables the use of an alternate electrical test method for PCB based QFP packages by making electrical contact through the robust BGA pads instead ofthe QFP leads.

  A more robust test procedure is achieved by elim- inating the molded carrier ring and designing the QFP leadframe with an array of metallized pads on the underside of the PCB. Figure 1 shows the top and bottom view of the leadframe in addition to a cross section. The array of pads are routed to the peripheral QFP leads through metallized vias. The PCB looks like a standard BGA on the bottom. The top of the board contains the signal traces which extend from the wirebond pads to the pads where the external leads are solder attached.

The package leads are joined to the PCB signal traces and to the leadhame rails at the lead tips. No

dambars are required.

  The metallized vias around the periphery of the PCB drop from the top side signal traces down to the backside metallized traces which redistribute the signals to the array ofpads. TThe PCB can be single- or multilayer to accommodate PCB fabrication tech- nology, electrical shields can be added, etc.

  With this design, electrical test can be done using the BGA pads spaced anywhere from 1.0 mm to 1.5 mm apart, as opposed to the typical 0.65 mm or 0.5 mm QFP lead pitch. Reliable test contact is made to robust package lands using standard sockets currently available to test BGAs and PGAs.

D Motorola. Inc. ,994

The QFP manufacturing and final test sequence using the BGA test pads is as follows:

l

Diebond.

Wirebond.

Encapsulate the die and wirebonds.

Trim lead tips from the leadframe rails.

Electrical test using the BGA area array pads instead ofthe peripheral leads.

Form the leads.

Excise the outer leads From the leadframe rails.

  Potential variations include Direct Chip Attach in place ofdiebond and wirebond, replacing the mold compound or potting material with a lid, etc.

  The BGA version of the design results from the elimination of the leadframe element used to form the peripheral leads of the QFP version. The identi- cal PCB based QFP design with area array test con- tacts can be used in the transition from a QFP to a BGA.

The manufacturing flow for the BGA version of the design is as follows:

l

l

l

l

l

l

l

Diebond.

Wirebond.

Encapsulation ofthe die and wirebonds.

Singulate the BGAs by removing the periph- ery of the PCB and the lead tips bonded to it. (F...