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AN1580 Datasheet(PDF) 2 Page - Motorola, Inc |
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AN1580 Datasheet(HTML) 2 Page - Motorola, Inc |
2 / 4 page 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 |
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Similar Description - AN1580 |
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