barcode scanner code in c#.net Number of reflow cycles in Software

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Number of reflow cycles
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235 260 C 6
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5 4 3 2 1
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mm 0.80 1.60 2.40 3.20 4.00 4.80 5.40 6.20 7.00 Inches 0.031 0.062 0.093 0.125 0.157 0.188 0.212 0.244 0.275
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mm 0.80 1.60 2.40 3.20 4.00 4.80 5.40 6.20 7.00 Inches 0.031 0.062 0.093 0.125 0.157 0.188 0.212 0.244 0.275
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PWB Thickness
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FIGURE 11.10 Charts for product D (phenolic 175 C Tg FR-4).
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SELECTING BASE MATERIALS FOR LEAD-FREE ASSEMBLY APPLICATIONS
Peak reflow temperature Please consult the PWB Design considerations section before using this tool 210 235 C 6
Number of reflow cycles Number of reflow cycles
235 260 C 6 5 4 3 2 1
mm 0.80 1.60 2.40 3.20 4.00 4.80 5.40 6.20 7.00 Inches 0.031 0.062 0.093 0.125 0.157 0.188 0.212 0.244 0.275
5 4 3 2 1
mm 0.80 1.60 2.40 3.20 4.00 4.80 5.40 6.20 7.00 Inches 0.031 0.062 0.093 0.125 0.157 0.188 0.212 0.244 0.275
PWB Thickness
FIGURE 11.11
PWB Thickness
Charts for product E (non-dicy, non-phenolic material with improved electrical performance).
to make some general recommendations that also take material cost into consideration. Figure 11.12 summarizes the cost versus performance recommendations for materials A through D in lead-free applications. Where improved electrical performance is required, product E should be considered.
FR-4 Grade product recommendations Peak reflow temperature range: 235 260 C Please consult the PWB Design considerations section before using this tool
Number of reflow cycles
5 4 3 2 1
mm 0.80 Inches 0.031
Product A
Product B Product D
1.60 0.062
2.40 0.093
3.20 0.125
4.00 0.157
4.80 0.188
5.40 0.212
6.20 0.244
7.00 0.275
PWB Thickness
FIGURE 11.12 Summary of recommendations in lead-free assembly for materials A through D.
PRINTED CIRCUITS HANDBOOK
EXAMPLE APPLICATION OF THIS TOOL
A simple example helps illustrate the practical application of this tool. This example is based on a real PCB design that was being converted to a lead-free assembly process. Some key features of the PCB as they relate to how it differed from a typical PWB as defined in Fig. 11.4, and the recommended adjustments suggested, are shown in Table 11.4.
TABLE 11.4 Example of a PWB Being Converted to Lead-Free Assembly PWB Design Feature Thickness Number of Reflows Material Surface Finish Recommended Adjustment Treat as an additional reflow cycle Consider moving up and right on chart
Attribute 1.60 mm (0.062 inches) 3 Conventional 140 C Tg FR-4 Lead Free HASL (HASL not Typical) 10(</=8 Typical)
Layer Count
Figure 11.13 shows the results of making the adjustments suggested, and shows that this material is not recommended for this application. Figure 11.12 recommends that product B be used in this application, and empirical evidence has shown that when the standard 140 C Tg material was used, some level of assembly-related defects was observed. When product B was used, no assembly-related defects were experienced.
Product A: Conventional 140 C Tg FR-4 Peak reflow temperature range: 23 5 260 C Please consult the PWB Design considerations section before using this tool
6 5 4 3 2 1
mm 0.80 Inches 0.031
FIGURE 11.13
Number of reflow cycles
Layer count HASL
1.60 0.062
2.40 0.093
3.20 0.125
4.00 0.157
4.80 0.188
5.40 0.212
6.20 0.244
7.00 0.275
PWB Thickness
Example of practical application of the selection tool.
SELECTING BASE MATERIALS FOR LEAD-FREE ASSEMBLY APPLICATIONS
11.5 DISCUSSION OF THE RANGE OF PEAK TEMPERATURES FOR LEAD-FREE ASSEMBLY
As was discussed in Chap. 11 in the context of decomposition temperatures, lead-free assembly temperatures represent a very critical range for many base materials. In the selection charts discussed in Sections 11.3 and 11.4, the lead-free temperature range is given as 235 to 260 C. Although some lead-free applications may fall outside this range, the bulk will likely fall within it. However, with respect to the impact on base materials, 235 to 260 C is a broad range. While this represents a range of only 25 C, for some materials an increase of only 10 C could be the difference between success and failure. Much more data must be gathered before more specific recommendations can be made, but Table 11.5 provides some very general guidance when selecting FR-4 materials such as those discussed in Sections 11.3 and 11.4 for two different ranges of lead-free assembly peak temperatures. All the other variables discussed up to this point must be considered as well, so once again, it is recommended that the user validate the material recommendations suggested here.
TABLE 11.5 General Recommendations by Lead-Free Peak Temperature Range Category Conventional 140 C Tg FR-4s 230 to 245 C Peak Temperatures May be suitable for PCBs of limited thickness and complexity where a limited number of thermal cycles will be experienced. Generally not recommended; even though initial results may be positive, extended storage in an uncontrolled environment prior to assembly could lead to problems. Suitable for a broad range of applications because of the higher decomposition temperature and overall thermal expansion being similar to standard high-Tg materials. Compatible in the broadest range of designs and applications. Recommended when long-term reliability is critical. 246 to 260 C Peak Temperatures Generally not recommended, but may be suitable for low-technology applications where a limited number of thermal cycles will be experienced. Not recommended.
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