p and bottom compliant Pogo pin contacts and mounting plate hardware.
Optionally, it has a backing plate.
The general items associated with an integrated circuit device that is testable and removable are as follows:
A PCB that connects the device to the correct functions and power sources enabling analysis of the devices
performance.
A device BGA socket that allows for multiple insertions of a single device into the same PCB circuit for use
or testing.
The high performance socket consists of two basic parts, the lid and body of the socket. The lid has a
spring-loaded plate that applies force to the top surface of the device-under-test, which causes the
connection balls on the bottom of the device-under-test to come in contact with and compress the socket
bases Pogo pin tips. The result is a mechanical and electrical connection between the device-under-tests
solder balls and the Pogo pins top plunger tips in the BGA socket.
The mechanical and electrical connection continues from the device-under-test top of the socket base to
the bottom of the socket base to the PCB thus providing the required functional and power connections.
The connections are made when the socket body's bottom Pogo pin tips are compressed against the PCB
as the socket body is screwed down onto the PCB.
QuickLogic® Application Note 91
Mounting a High Performance BGA
Socket on a Printed Circuit Board www.quicklogic.com
© 2007 QuickLogic Corporation






Mounting a High Performance BGA Socket on a Printed Circuit Board Rev. A
2
Figure 1: Compression Fit Socket Mechanical Drawing © 2007 QuickLogic Corporation
www.quicklogic.com






Mounting a High Performance BGA Socket on a Printed Circuit Board Rev. A
3

Table 1
provides a description of the numbered items in
Figure 1
.
Socket Description
The Mounting Forces Associated with BGA Pogo Sockets
The Pogo pin employed in the BGA socket is a dual-compliant piston style structure, meaning that each end of
the Pogo pin has a built-in spring-forced position compressible plunger assembly (see item (5) in
Figure 1
).
Each end of the Pogo pin can adapt to a mating surface plane and adapt its contact profile to account for small
nonplanar tolerances of the mating surface. For example, if on one side of the Pogo pin all the pads associated
with the PCBs socket footprint are not co-planar to the surface, and on the other side of the Pogo pin the
devices leads are not co-planar to the surface, each end of a Pogo pin can independently compress its physical
length to adapt to each non-planar surface.
The Pogo pin has a specification to describe its length, width, compression travel distance, and grams of
contact pressure. Typical compression forces are between 10 grams to 20 grams (0.353 ounce to
0.706 ounce) of contact pressure, which compresses each of the Pogo pistons to about one-half of their travel
distance and alters the Pogo pins length.
For example, if a socket has 196 Pogo pins with a compression force of 10 grams per pin, its total
compression force is about 1960 grams, which translates to approximately 4.325 pounds of force needed for
the socket to mate properly with its interface (i.e, a PCB and a device). Therefore, the contact mounting force
between the socket and the PCB is approximately 4 pounds, and independently, the contact force between
the device and the socket is also a separate 4 pounds approximately; the two forces do not interact. This is
the function of a dual-compression Pogo pin.
The mounting arrangement of the socket to the PCB must be able to tolerate this mounting force without
deformation by either a thick PCB or use of the optional socket backing plate (9).
Table 1: Parts List
Item No.
Description
1
Socket lid
2
Screw (4)
3
Device-under-test
4
Socket base
5
Pogo pin
6
Pogo pin retainer plate
7
Retainer plate mounting screw (2)
8
PCB
9
Pogo pin compression pressure backing plate
10
Washer (4)
11
Mounting screw (4)
12
Non-dimensioned PCB footprint for a typical BGA socket
13
Cross-sectional view of the socket assembly www.quicklogic.com
© 2007 QuickLogic Corporation






Mounting a High Performance BGA Socket on a Printed Circuit Board Rev. A
4
The Mounting Surfaces Associated with BGA Pogo Sockets
NOTE:
The following references that are noted as (n) are in reference to Figure 1 items (1) through (13).
To ensure a high quality and reliable connection, the conditions of the device and the PCB associated with the
socket must be considered as part of the connection system:
The PCB footprint (12) of the socket interface has an indicated keep out area which must be free of
obstructions such as surface mounted components.
The PCB target connection pads must be free of solder-mask material, oxides, or any other contaminants
to ensure an electrical connection.
The solder-mask thickness and build-up height associated with the area of the PCB socket site must not
exceed 2.0 mils (see enlarged view of item (8) in
Figure 1
). The sockets bottom mounting surface is bolted
to the top of the solder mask. The Pogo pin protruding from the bottom of the socket has a limited height
offset and compression distance (see item (5), Pogo pin bottom plunger). Therefore, to ensure a reliable
electrical connection between the socket and the PCB contact lands, the solder mask thickness must not be
greater than the compressed contact length of the sockets bottom Pogo pin (see individual socket data
sheets for dimensions).
The PCB target connection pads must be planar to within ±0.5 mils, i.e., if a via drill hole is located in the
target pad area, that hole must be backfilled to be planar with the PCB pad.
When mounting the BGA socket onto the PCB, use only enough screw force to ensure correct connection
between the socket and the PCB. Be aware that PCB warping or bowing can be caused by a thin PCB, an
obstruction existing between the socket and the PCB, or over-tightening the socket mounting screws. Also,
be careful not to strip the threading in the socket base by over-tightening the screws.
NOTE:
To ensure a positive mounting pressure for the socket to PCB interface (see items (4), (8), (10),
and (11) in Figure 1), take into consideration that the screws are a fixed length, three threads go into
the socket, and the thickness of the PCB and washers, comprise the remaining length of mounting screw
(11). A Pogo pin compression pressure backing plate (9) is necessary if the PCB is too thin to prevent
PCB warping
The devices connection balls must be free of contamination and planar in alignment.
BGA Socket Mounting Procedure
To mount a BGA socket onto a PCB that has had its connection lands previously soldered, additional steps
are required to ensure the best possible inter-connection:
1.
Clean all excess solder from the connection lands using a solder-wicking technique.
2.
Clean all material from the connection land sites of the PCB so that the lands have no contaminants,
material debris, or excess solder. When done, the PCB contact points should have a bright and shiny solder
appearance, not dull or rough.
3.
Verify that the area between the connection lands of the PCB area do not have any solder-bridging between
them, since this will cause unwanted shorts.
4.
Ensure that all the connection lands are planar to each other within ±0.5 mils.
The BGA socket and PCB are ready for device insertion and electrical use.

After a reasonable use interval, or
if connection problems occur, repeat steps 1. through 4. © 2007 QuickLogic Corporation
www.quicklogic.com






Mounting a High Performance BGA Socket on a Printed Circuit Board Rev. A
5

Device Application Test Considerations
This section discusses the factors affecting a good and reliable connection between a high performance BGA
compression socket and an end users application PCB board for the purposes of product demonstration and
debugging.
Figure 1
shows various expanded views of the significant components in a high performance double
compression socket and its environment, which is suitable for use as an applications debugging platform for
QuickLogic devices.
Device to Socket Mounting Considerations
NOTE:
The following references noted as (n) are in reference to Figure 1 items (1) through (13).
As shown in
Figure 1
, item (1) is an aluminum socket lid with a built-in spring-loaded top floating plate that
acts as a compression base that pushes down onto the top surface of the device-under-test (3). The internal
body of the socket lid (1) has four screws (2) that fasten to the top of the socket base (4).
Once the socket lid screws (2) are fastened to the socket base (4), the socket lid (1) can be installed or removed
by a quarter turn of the socket lid screws (2) relative to the socket base (4). The device-under-test (3) lies
between the spring-loaded floating plate of the socket lid (1) and the socket base (4), with the devices
connection solder balls connecting to protruding Pogo pin (5) top plunger tips. Reasonable force is required
to make this connection since the downward compression of all the Pogo pins (5) is pushing against the
device (3) and the socket lid (1) of the assembly.
The Pogo pins (5) are housed in the socket base (4) and are kept in place by the attachment of the Pogo pin
retainer plate (6) using two screws (7).
An enlarged detail cutaway drawing of the Pogo pin (5) shows that it is comprised of three elements:
Shell of the Pogo pin.
Top plunger assembly that has a crown point tip for good BGA device ball mechanical and electrical
connections.
Bottom plunger assembly that has a chisel point tip for good PCB