Hot Air Reflow with HASL

[JustMeHere]

Does anyone have experience hot air soldering HASL boards? 

I've read that it is not good because of its uneven surf.  When I do solder my ENIG boards, I've found it easiest to pre tin the pads of the small chips, flux, place the chip, then reheat what is there.   It seems like HASL would save me a step. 

The chips are like 16QFN.  I do mostly try to stick to SOIC chips though.

[bson]

Depends a lot on the HASL.  With some boards and footprints, especially 0.5mm and 0.65mm SOP/LQFP, the pins often end up balancing on top of the tin and are really prone to shifting sideways.  Tin and paste is pretty slippery.  Also makes it hard to nudge a package to center it since you're effectively pushing uphill.  But, yeah, less paste is needed with HASL than ENIG and it's no problem for passives or larger footprints that effectively have flat surfaces.  The thickness of the HASL layer also varies.

[anvoice]

I've hot air soldered QFN packages with HASL, but I have applied extra solder. HASL is meant to protect the boards, not to provide an alternative for solder paste/solder, so I'm not sure if there's enough to make a good joint. As bson said, probably depends a lot on the HASL thickness.

[perieanuo]

I've hot air soldered QFN packages with HASL, but I have applied extra solder. HASL is meant to protect the boards, not to provide an alternative for solder paste/solder, so I'm not sure if there's enough to make a good joint. As bson said, probably depends a lot on the HASL thickness.

Meetoo
You apply solder evenly on the qfn pads then you place your chip, no matters it is industrial or home edition, iron of hot air or whatever.
Regards,pierre,qfn and bga welder


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[mrpackethead]

If you are hand soldering your boards. then theres not a lot to be gained using ENIG over HASL. 

The primary reason for using ENIG Is that it provides a much flatter surface than HASL, and that is very useful when you are doing fine pitch parts were you need to get high precision prints with your solder stencils.  Small height variations on the board create variances which in turn result in addition faults.       Its also benefical for parts like QFNS, as the center pad wont' sit flat.

[JustMeHere]

Thanks all.  I can get 10 HASL boards for the same price I can get 3 ENIG.  Sounds like either way I'm going to be prepping the pads for the fine pitched parts. 

[mrpackethead]

Theres another reason for ENIG that i forgot.   If your boards are HASL, you will end up with two types of solder. The solder that the PCB fab used, and the solder you do. In some cases, this is a problem, in others not a problem..

With QFN Chips using HASL will have the effect of considerably increasing the defect rate,  THough if you are handsoldering this, then i probalby wont' make much differences. Are you using a hand held hot air source to reflow it?

[JustMeHere]

 Yes, I use hand held hot air.

I've had the best results with thinning everything with a slight pillow.  Really just enough so you can feel bumps but not really see them with the naked eye.  I also carefully do the center pad.  Then I swipe once with flux.  Finally, I place the chip.

I heat the area until I think I see the chip center up.  Next, I tap the chip directly down to help make sure everything is connected.  This helps with the surface not being exactly even.   To confirm, I nudge the chip very gently to see if it snaps back into place.  If so, things must be good.

Next I inspect with a loupe and a microscope.  If I see something isn't connected, I touch up with a iron.