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QFP Coplanarity & Alloy 42

Arturo

#25892

QFP Coplanarity & Alloy 42 | 30 September, 2003

Does alloy 42 lead frame on a QFP100 make lack of coplanarity (let's say 2 mils), a critical factor to have non-wetted leads?

Lead coating is tin lead 90/10.

afm

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#25894

QFP Coplanarity & Alloy 42 | 30 September, 2003

We're not clear on what you seek. So, as a starting point for our discussion, we wouldn't get agitated if we saw "routine" coplanarity of 4 thou.

For instance: Maximum Lead Coplanarity [Altera] Package||Acronym||Lead material||Finish||Maximum Lead Coplanarity Plastic dual in-line||PDIP||Copper||Solder plate|| Ceramic J-lead chip carrier||JLCC||Alloy 42||Solder dip||0.006 inches (0.15 mm) Plastic J-lead chip carrier||PLCC||Copper||Solder plate||0.004 inches (0.10 mm) Ceramic pin-grid array ||PGA||Alloy 42||Gold over nickel plate|| Plastic small-outline integrated circuit||SOIC||Copper||Solder plate: 100-pin commercial, Solder dip: 208-pin|| Plastic quad flat pack||PQFP||Copper||Solder plate|| QFP packages with a lead pitch of 0.65 mm or greater||||||||0.004 inches (0.10 mm) QFP packages with a lead pitch of 0.5 mm||||||||0.003 inches (0.08 mm) QFP packages with 208 pins or greater||||||||0.003 inches (0.08 mm) CQFP packages with a lead pitch of 0.5 mm||||||||0.004 inches (0.10 mm) Plastic thin quad flat pack||TQFP||Copper||Solder plate|| Power quad flat pack||RQFP||Copper||Solder plate|| Ball-grid array||BGA||Tin-lead alloy (63/37)||||0.008 inches (0.20 mm)

Do those leads take solder in a standard J-002 "dip & look" solderability test?

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Arturo

#25899

QFP Coplanarity & Alloy 42 | 1 October, 2003

They take the solder in a dip and look solderability test but when in normal reflow process we got some pins that do not get wet and the appearance is as follows: -Pillow effect on the toe(no front fillet is formed) -There is a sheet of flux between the bottom of the lead and the top of the solder that cracks and turns white if we move the pin. -No heel fillet is formed. -We got 95% pad coverage with a 6mil electroformed stencil and a well formed brick.

Time above 183�C has been increased up to 105 secs and peak up to 230�C but the problem still appearing.

Spec for coplanarity on this QFP is 4 mils.

afm

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#25901

QFP Coplanarity & Alloy 42 | 1 October, 2003

You're thinking correctly.

Concentrate your recipe development efforts by profiling directly on the pads [that some fine designer forgot to thermally isolate properly] of those pesky corner leads that don't solder well.

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