> Do you mean 9 pads instead of 8? (A picture would be worth a thousand > words here) ..
I've attached an image of the gerber layers for a 32 pin MLF. Last time I tried attaching an image Yahoo Groups filed it and provided a link, so hopefully it'll do that again. I've emailed a copy direct to you too in case it doesn't work out. Note there are 8 pads surrounding a (square-tented) via, so there will be eight small squares of solder, rather than one big one (which can cause the package to float). BTW, if you look closely you'll notice a narrow area around the edge of each pad. That's where I shrunk the solder paste to reduce problems when soldering. >> The use of a tented via in this way means that the via will be >> solidly connected to the heatsinking copper zone on the reverse >> side, whilst the tenting prevents solder wicking through the via. > > I'm not sure I understand exactly -- do you mean the solder sicking > would move enough solder to float the chip? No - there are two causes of poor bonding specific to MLF and similar. One is that the solder forms a large blob on which the chip floats, lifting the chip's legs above the solder on the pads around the outside. This can also result in the chip drifting off centre or rotating. The other cause is solder going through the thermal via by capillary action, reducing the expected quantity of solder available for the thermal pad. > I'm thinking you might mean that the pads break up the area ( sort of > a star shaped area) so with smaller blobs the chip floats less? Correct, because now you have 8 small hillocks rather than one big hill (if that makes sense). Something resting on eight points is more stable than something resting on one. > http://wiki.xtronics.com/index.php/Pcbnew#Preventing_Thermals_on_heatsinking_pads_of_SM_packages I'll try and take a look later/tomorrow. It's the end of another longer hard day at the PC :). Regards, Robert.
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