PCB ASSEMBLY GUIDELINES The purpose of this document is to provide users with guidelines for use of Exar’s surface mount devices classified to the levels defined in J-STD-020. SOLDER REFLOW PCB (printed circuit board) assembly involves attaching ICs and other components to PCB's by applying heat or thermal energy to solder component’s terminals to PCB’s contact pads. Solder material is introduced to the joints through solder paste printing or wave soldering. The “solder reflow” is achieved when an appropriate amount of heat or thermal energy is applied to raise the temperature of the solder above its eutectic melting point. Upon completion of the solder reflow and cool-down, a solid solder joint is formed with proper mechanical strength, metallurgical structure, and electrical conductivity. REFLOW PROFILE & CONTROLLED HEATING Solder reflow profile should be properly designed and evaluated by the PCB assembly process engineer based on solder paste, heating method, PCB design, thermal mass of the entire board and component sensitivity. During reflow, the component body temperature must not exceed the rated value stated on the caution label. Typical solder reflow profile requirements are listed in Tables 1, 2 and 3 and illustrated in Figure1. Table 1: Reflow Temperature Parameters Profile Feature Preheat/Soak Temperature Min (TSMIN) Temperature Max (TSMAX) Time (tS) from (TSMIN to TSMAX) Ramp-up rate (TL to TP) Liquidous temperature (TL) Time (tL) maintained above TL Peak package body temperature (TP) Time (tP)* within 5 °C of the specified classification temperature (TC) Ramp-down rate (TP to TL) Time 25 °C to peak temperature Sn-Pb Eutectic Assembly 100 °C 150 °C 60-120 seconds Pb-Free Assembly 150 °C 200 °C 60-120 seconds 3 °C/second max. 183 °C 60-150 seconds See Table 2 20 seconds (Note 1) 3 °C/second max. 217 °C 60-150 seconds See Table 3 30 seconds (Note 2) 6 °C/second max. 6 minutes max. 6 °C/second max. 8 minutes max. Notes 1. Tolerance for peak profile temperature (TP) is defined as a supplier minimum and a user maximum. 2. All temperatures refer to the center of the package, measured on the package body surface that is facing up during assembly reflow (e.g., live-bug). If parts are reflowed in other than the normal live-bug assembly reflow orientation (i.e., dead-bug), TP shall be within ± 2 °C of the live-bug TP and still meet the TC requirements, otherwise, the profile shall be adjusted to achieve the latter. To accurately measure actual peak package body temperatures, refer to JEP140 for recommended thermocouple use. Table 3: Pb-Free Process – Peak Reflow Temperature (TC) Package Volume Volume mm3 Volume 350-2000 mm3 >2000 Thickness mm3 <350 < 1.6 mm 260°C 260°C 260°C 1.6-2.5mm 260°C 250°C 245°C >2.5 mm 250°C 245°C 245°C Table 2: SnPb Eutectic Process – Peak Reflow Temperature (TC) Volume Package Volume Thickness mm3 <350 mm3 ≥350 < 2.5 mm 235°C 220°C ≥ 2.5 mm 220°C 220°C Rev 1.0 Page 1 AAN-00000002 Figure 1: Typical Reflow Profile Rev 1.0 Page 2 AAN-00000002