AN1580

2

MOTOROLA RF APPLICATIONS REPORT

The package’s 16 leads are manufactured to be coplanar

within a 0.10 mm (.004

″) tolerance (see Figure 1). The bottom

surfaces of the 16 feet will be no more than 0.10 mm (.004

″)

above the seating plane (see Datum C in Figure 4), defined as

the plane furthest from the center of gravity, and common to

three of the package feet that surround the center of gravity.

Simply, when the package is placed feet first (down) on an

ideally flat plane, no foot will be more than 0.10 mm above the

plane.

Figure 1 uses exaggerated lead lengths to demonstrate

more clearly acceptable tolerances. Leads 1, 2, 4, 5, 6, and 7

are all depicted ideally coplanar with the basis plane. Leads

3 and 8 are marginally acceptable at the extreme edge of the

tolerance.

Figure 2 displays the standoff specification and how it

controls height of the metallic heat sink above the seating

plane. The bottom surface of the metallic heat sink must not

be lower than 0.025 mm (0.001

″), nor may it be lower than the

bottom of the highest lead, (highest possible lead is limited by

the coplanarity condition at 0.10 mm or 0.004

″) and it may not

be higher than 0.152 mm (0.006

″) above the seating plane.

The foot angle specification requires the toe end of the foot

of the lead to be lower than the heel end by 0 to 8

°, as

referenced from the seating plane. See Greek symbol Theta

(

θ) in the Package Outline Dimension table in Figure 4.

These three specifications ensure that the manufacturer

receives

reflow

solderable

products.

The

coplanarity

specification ensures that all of the leads on the package will

be solderable to a PC board with a proper solder reflow

process. It also helps increase the repeatability and reliability

of a manufacturer’s reflow processes. The standoff restricts

the solderable pad above the basis plane and places it no

lower than the highest lead. It also creates space to clean off

the residual flux resin. Finally, the foot angle specification

allows for smoother solder fillets between the lead and the PC

board. These specifications all make the package more

solderable, reduce solder defects and rejects, and help

provide longer life solder joints, as well as provide a very

durable product for the customer.

MOUNTING/SOLDERING CONSIDERATIONS

Soldering the PFP–16 to a PC board requires no more

equipment than most

other surface mount packages.

However, due to the backside contact, some precautions

about how the equipment is used to produce quality solder

joints are necessary. The soldering recommendations that

follow are provided solely for the convenience of the

manufacturer and are not sufficient for actual manufacturing

processes due to variations from process to process.

The PFP–16 package is intended to be placed onto solder

paste that is 0.15 mm (0.006

″) high and on a PC board with an

overstroke of 0.10 mm (0.004

″). These values are to be

considered as suggested values only.

An overstroke of 0.10 mm is created by setting the

placement piston of a “pick and place” machine not only to

push the part off of the vacuum head and onto the PC board

but also to continue its quick motion and push the part an extra

0.10 mm into the PC board, and then release. This is an

intended part of the package design so that the bottom surface

of the metal heat sink will get pushed into contact with the

solder paste that is already on the PC board. This process

should leave solder clinging to the bottom surface of the

backside contact, which, when reflowed, should result in a

quality solder joint as shown in Figure 3.

The PFP–16 has been successfully soldered to a PC board

using many different reflow techniques (infrared, hot stage,

etc.). Specifications for soldering and reflowing the PFP–16

depend on many external factors such as board mass,

component density, and reflow methodology. It is important to

note that most solder liquidus temperatures are higher than

the rated exposure temperatures of the package and

semiconductor devices, and under such conditions, damage

to the part may result. Consequently, customers are cautioned

against exposing the package to high temperatures for

extended periods of time. The following are suggested values.

Figure 3. Effect of Overstroke

NORMAL

LEAD

POSITION

NORMAL

LEADS

FLEXING

OUT

OVERSTROKE

NORMAL PLACEMENT

PRINTED CIRCUIT BOARD

HEAT SINK FORCED INTO SOLDER