Issue link: https://iconnect007.uberflip.com/i/1293772
OCTOBER 2020 I SMT007 MAGAZINE 61 ture was 150–200°C for 105 seconds. For Pro- file C, the preheat temperature was 150–205°C for 120 seconds, with time between 180°C and 205°C at 80 seconds. All profiles were run in air atmosphere. In addition, for Profile B, a nitro- gen atmosphere (1000ppm O 2 ) was also used to evaluate the difference in spattering occur- rence by variation of the reflow atmosphere. The Occurrence of Flux Splattering Based on the Variation of Stencil Thickness in the Reflow Oven The occurrence of flux splattering on the copper plate using conventional Sn3Ag0.5Cu no-clean Type 4 Paste A based on different stencil thicknesses of 0.1 mm, 0.15 mm, and 0.2 mm were investigated using Profile B in air reflow atmosphere. The stencil aperture open- ing was 6.5-mm diameter. Developed Paste Product C Flux Splattering Evaluation Using the Reflow Oven and Simulator A new Paste Product C was developed to reduce flux splattering [1] . Type 4 lead-free Sn3Ag0.5Cu Paste Product C was compared to the conventional no-clean Type 4 Paste Prod- ucts A and B, using Profiles A, B, and C in the air reflow atmosphere in the eight-heat-zone production reflow oven. Also, the reflow simu- lator was used to compare the flux splattering behavior of the Paste Product C versus conven- tional Paste Product A. Additional Testing of Paste Product C In addition to the flux splattering tests, tests were done with Paste Product C to understand its general printing and reflow performance in production. Testing included continuous paste printing tests on a company test vehicle on 0.4-mm pitch QFP board pads. For the printing evaluations for the 0.4-mm pitch QFP, the board pads were 0.2 mm in width and 1.5 mm in length with the distance between pads at 0.2 mm. The thickness of the laser-cut stencil was 0.12 mm. The produc- tion printer speed was 40 mm/sec. The paste was inspected at time zero and after 200 print strokes. For meltability testing, evaluations were con- ducted on the company test vehicle (Figure 5) on 0.25-mm diameter CSP board pads and 0603 pure tin-coated chip resistor components reflowed using Profile A in air atmosphere on boards with ENIG board surface finish. For reflow/voiding assessment, the evaluations were conducted on the same test board on pure tin-coated power transistor (BTC/QFN), pure tin-coated 6330 resistor, and 1-mm pitch Sn3Ag0.5Cu BGA components in air atmo- sphere using Profile A. Results and Discussion Timing of the Occurrence of Flux Splattering Using the Reflow Simulator Equipment It was confirmed that splattering rarely occurs during preheating and occurs mainly Figure 5: Company test vehicle used for additional testing on Paste Product C. Figure 4: Reflow profiles used.