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ACPM-7886-TR1 Datasheet(PDF) 9 Page - AVAGO TECHNOLOGIES LIMITED |
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ACPM-7886-TR1 Datasheet(HTML) 9 Page - AVAGO TECHNOLOGIES LIMITED |
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9 / 14 page  9 Lead Free Reflow Profile General Guidelines i. Ramp 1 Ramp to 100°C. Maximum slope for this zone is limited to 2°C/sec. Faster heating with ramp higher than 2°C may result in excessive solder balling and slump. ii. Preheat Preheat setting should range from 100 to 150°C over a period of 60 to 120 seconds depending on the charac- teristics of the PCB components and the thermal charac- teristics of the oven. If possible, do not prolong preheat as it will cause excessive oxidation to occur to the solder powder surface. iii. Ramp 2 The time in this zone should be kept below 35 seconds to reduce the risk of flux exhaustion. The ramp up rate should be 2°C/sec from 150°C to re-flow at 217°C. It is important that the flux medium retains its activity during this phase to ensure the complete coalescence of the solder particles during re-flow. iv. Reflow The peak reflow temperature is calculated by adding ~32°C to the melting point of the alloy. Lead free solder paste melts at 218°C and peak reflow temperature is 218°C + 32°C = 250°C (±5°C). Note that total time over 218°C is critical and should typically be 60 – 150 seconds. This period determines the appearance of the solder joints. Excessive time above reflow may cause a dull finish and charred of flux residues. Insufficient time above reflow may lead to poor wetting and improperly fused (cloudy) flux residues. Figure 3. PCB land pattern Figure 4. Stencil outline drawing Figure 5. Combined PCB and stencil layouts v. Cooling Maximum slope for cooling is limited to 3°C/sec. More rapid cooling may cause solder joints crack while cooling at a slower rate will increase the likelihood of a crystalline appearance on the solder joints (dull finish). PCB Design Guidelines The recommended ACPM-7886 PCB land pattern is shown in Figure 3. The substrate is coated with solder mask between the I/O and conductive paddle to protect the gold pads from short circuit that is caused by solder bleeding / bridging. Stencil Design Guidelines A properly designed solder screen or stencil is required to ensure optimum amount of solder paste is deposited onto the PCB pads. The recommended stencil layout is shown in Figure 4. The stencil has a solder paste deposi- tion opening that is approximately 80% of the PCB pad. Reducing the stencil opening can potentially generate more voids. On the other hand, stencil openings larger than 100% will lead to excessive solder paste smear or bridging across the I/O pads or conductive paddle to adjacent I/O pads. Considering the fact that solder paste thickness will directly affect the quality of the solder joint, a good choice is to use laser cut stencil composed of 0.100mm (4 mils) or 0.127mm (5 mils) thick stainless steel which is capable of producing the required fine stencil outline. The combined PCB and stencil layout is shown in Figure 5. (dimensions in mm) 2.1 0.375 0.55 0.375 1.68 0.64 0.64 0.44 2.1 1.68 0.55 Stencil Opening 0.44 |
Similar Part No. - ACPM-7886-TR1 |
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Similar Description - ACPM-7886-TR1 |
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