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Subject:	Re: Reflow profiles for mixed Pb status boards
From:	Ioan Tempea <[log in to unmask]>
Reply To:	(Designers Council Forum)
Date:	Fri, 26 Jun 2009 12:08:09 -0400
Content-Type:	text/plain
Parts/Attachments:	text/plain (65 lines)

Gary,

Unless you have BGAs on your board, the leaded boards will be soldered at tin-lead specific temperatures, which is 208 to 220 C, depending on the board finish, regardless of the RoHS compliance or non-compliance. Lead-free components will solder very well at leaded temperatures.
If lead-free BGAs are on the boards, the temperature will have to go up in the range of 220-225 C, in order to get reliable joints on this component.

I advise you to state on the assembly drawing the soldering alloy you want (SnPb or lead-free), as well as the flux chemistry you require (RMA, water soluble, no-clean). These 2 factors are very important to communicate to your assembler.

Regards,

Ioan Tempea, ing.
t : 450-967-7100 ext : 244
[log in to unmask]
www.digico.cc
P N'imprimer que si nécessaire - Print only if you must
-----Message d'origine-----
De : Gary Koven [mailto:[log in to unmask]]
Envoyé : 26 juin 2009 11:35
À : [log in to unmask]
Objet : [DC] Reflow profiles for mixed Pb status boards

We have a number of PCBAs with both leaded and lead-free parts on them.

Looking over the J-STD-020 reflow profiles on one of the leaded part datasheets, we saw that its range seemed too restrictive for the lead-free profile.

Basically the two parameters that interest us are:

(1) Preheat temperature, 100 oC-150 oC for leaded and 150 oC-200 oC for lead-free.

(2) Liquidous temperature, 183 oC for leaded and 217 oC for lead-free.

On our assembly drawings we call out IPC-A-610 Class 2. I understand that J-STD-002 can also be used together with IPC-A-610 as a note callout.

Since there is not a RoHS-compliant requirement for these boards, we don't call out what type of solder process needs to be used.

We're curious about how assembly shops adjust their soldering process for boards that have both types of parts on them.

We're also wondering whether we need to begin calling out specific solder processes, but we don't want to add cost to the assembly.

Give me a solution that doesn't add cost to the assembly, but at the same time satisfies the curious, please.

TIA and Best Regards,

Gary M. Koven, C.I.D.
Dynazign, Inc.
Charlotte, NC, USA
Veteran of the Marsh School

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