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Fine Pitch Pad Width Size VS Component Lead Width

Dreamsniper

#5919

Fine Pitch Pad Width Size VS Component Lead Width | 11 April, 2001

Hi,

We got a 0.5mm pitch QFP144 from Altera with the below lead width specs.

min. lead width = 0.17mm nominal = 0.22mm maximum = 0.27

What's the best pad or land width for the above?

This is what our designer used.

Land Width = Component Lead Width + 20% of that Component Lead Width

The problem is that some of the QFP leads are easily detached using a small amount for push force using a thin pick. I found out that the solder joint is not very strong because there is no solder fillet on the left and right side of the lead and the possible cause, which is very visible, is that the lead width is one-to-one with the land and in some cases you can no longer see the land / pad.

from the above land width calculation, which among the lead width value will he need to base his Component Lead Width, minimum ? nominal? or maximum? He told us that he used the nominal but it seems like we are getting QFP's with the maximum lead width. What's the best Land Width for the above manufacturer's lead width specification? Is IPC's Land Design Standard a best reference?

Thanks and regards,

Thanks to you DaveF in advance.... :=)

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#5920

Fine Pitch Pad Width Size VS Component Lead Width | 11 April, 2001

Hi Dreamsniper,

the IPC land design standard is IMO a good reference. If you use the online calculator you can influence the result by varying for example manufactoring parameters. For the same lead width and same tolerances (and of course pitch) we agreed on 0,3mm nominal pad width. Due to the fact of overetching we rarely get this nominal width realized on the actual boards. The minimum width is determined by agreement between us and the boardhouse according the percentage of allowable overetching.

1) you might check the pad width on the PCB 2) I read in a recent thread that Side fillet doesn�t add to much to the integrity of the joint 3) I�ve encountered similar things with QFP�s, handsoldering showed good results in that case and we found that these problems were actually caused by soldermaterials and reflow parameters. 4) Don�t try to compare finepitch pins with others regarding the shear force.

Hope that helps

Wolfgang

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