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Fine Pitch QFP100 Solder Joint - Need Help!



Fine Pitch QFP100 Solder Joint - Need Help! | 30 October, 2002

Hi Guys, I have a fine pitch QFP that I suspect of having a solderability (wetability) problem. The heel joint is 50%-75% of the lead thickness so it means that I passed the IPC Class 2 recommended criteria on the Heel. The toe has at least 25%-50% solder rise which means that it is good and acceptable but the side joint wetting is very minimal and almost zero. Some of the leads' side joints have very thin wettings. So to describe the photo, the solder joint looked like this: the heel joint(viewed in side view) which has a good wetting then the side joint with a very thin line of wetting which is just a shiny line between the pad and the lead bonding them together then the toe with a 25% solder rise. The side of the termination lead looked the same before and after reflow which i suspect to have oxidised. It seems like the flux did not activate and clean that area. Is it a sign of a bad joint? I have only a 4-zone Heller 1088 oven but we have been running fine pitch since 2 years ago and some of the fine pitch components have good wettings except for this QFP100 from Infineon which I suspect to have oxidised leads. I can provide you some photos for analisys if you just give me your e-mail add. My thermal profile is 213 - 223 deg. C with a dwell of 55 to 70 secs. measured on the four sides of that QFP. I'm using an Indium Paste NCQ92 with 2% silver. PCB is a four layer bd. with 60% of the bottom layer is a ground plane (copper). It's dimension is 145L x 160W.

Thanks and best regards,

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Randy V.


Fine Pitch QFP100 Solder Joint - Need Help! | 30 October, 2002

I would perform a simple solderability test per ANSI/J-STD-002. You can do this using a compatable no-clean flux like Indium NC771 and a solder pot. If the leads wet well you do not have a solderability problem. I did not notice what plating was on the board or if you are reflowing in Nitrogen or not but you may just be on the lean side as regards to total solder volume. The side fill is also dictated by how much copper is on each side of the lead. If its close to 1 to 1 you will not see a real fillet. Also, make sure one of your T.C.'s is mounted to the lead as the lead can be cooler or hotter than the board. The time above 183 degrees should be around 45 seconds although SN62 melts at 179C.

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Fine Pitch QFP100 Solder Joint - Need Help! | 30 October, 2002


Pls snd pix

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Fine Pitch QFP100 Solder Joint - Need Help! | 30 October, 2002

Is toe fillet still required?

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Fine Pitch QFP100 Solder Joint - Need Help! | 31 October, 2002

Toe fillets are not required per IPC, you can actually have toe overhang.


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