SMT资料ProfileGuidelines英文

1、profile guidelineshttp:/ heating ramp05010015020025015 3045 60 75 90 105 120 135 150 165 180 195 210 225 240 255 270 285 300time (s)temp (0c)initial heating ramp object is to get profile to pre-heat stage limited by board & components (thermal shock) explosive out-gassing from the solder paste will

2、only occur under extreme conditions (eg laser soldering) common ramp-rates are 1-3c.s-1this stays the same for lead free pre-heat soakpre-heat soak the pre-heat allows all areas of the board to reach a similar temperature before reflow with modern ovens it is possible to reduce or eliminate the “pla

3、teau” part of the profile there is no specific activation temperature for solder pastes. however the activators become more effective once they are molten or dissolved in molten resinpre-heat soak rosins begin to soften and flow at temperatures between 70- 120c a simple law of chemistry says that re

4、actions become faster at higher temperatures during the pre-heat (in aerobic reflow), oxidation will occur on exposed metal surfacespre-heat soak although the pre-heat soak for lead based alloys is considered to be between 100 150 centigrade. this will increase to 120 170 for pb free. the time remai

5、ns roughly the same at 90 150 seconds if a plateau profile is run we would recommend going from this to reflow spike as quickly as is safe to achieve.05010015020025015 3045 60 75 90 105 120 135 150 165 180 195 210 225 240 255 270 285 300time (s)temp (0c)reflow spikereflow spike this is when the sold

6、ering occurs all areas must exceed the melting point of the alloy to allow powder particles to coalesce, wet the surfaces and fill capillaries a higher temperature will lower the surface tension of the solder and increase the efficiency of the fluxreflow spike a higher temperature will increase oxid

7、e formation, discolour residues & board and may damge components a good reflow spike is usually about 30-40c above the liquidus of the alloy (eg. 210-220c for sn62) and will be above the melting point for 30-60 seconds for pb free this is also 30 60 seconds (90 in extreme soldering conditions. the t

8、emperature need only be from 232 245 depending on the medium used.solder solidification05010015020025015 3045 60 75 90 105 120 135 150 165 180 195 210 225 240 255 270 285 300time (s)temp (0c)solder solidification rapid cooling will give bright shiny joints slow cooling allows more dissolution of substrates which will give rough or dull looking joints. taken to extreme, this can lead to de-wetting and poor strength the boards should b