Earl,

>There can be no true thickness spec for HAL by process definition.

What about controlling the Air knife pressure? If the minimum thickness of
solder on any part of pads regularly comes in less than specified, lets say
1.5 microns, then if the pressure is reduced will it not increase the
quantity of solder left on the pad? We have used this in the past ourselves,
the supplier put a document on the Vertical Hasl bath, stating that our
boards should have a lower pressure reading on the gauge.

>Simply, it must be capable
>of supporting soldering operations, solder wetting, acceptable solder
joints, and long term
 >reliability. It often is not capable of doing so.

 We find no problems soldering to HASL boards after 4 years of storage.

If a fab shop tries to give a flat finish using HASL, then there can be
problems, ie. it can be too thin. For reliable storage a minimum thickness
should be specified. If you use HASL just accept that there's a solder dome
and give it a decent thickness. Too many shops are trying to give flat HASL
finish and compromising the reliability with regard to long term storage or
regarding multiple thermal cycles.
(Any data I've seen presented, shows solderabiltiy of HASL as better than
ENiIAu and OSP, after multiple thermal cycles.) I don't recall data for long
term storage, although this should pressumably be qualified with HASL
thickness. Come to think of it so should the Multiple Thermal Cycle data.


>This is why so many seek alternative solder
>termination area coatings.

Which alternative coatings retain superior solderability after long term
storage?

The only reasons I can see for seeking alternatives are lower SIR values,
(why can't the PCB industry use less aggressive/bromide free fluxes?) or the
desire to remove lead from the process. Direct contact to pads such as
connectors in mobile phones are another reason.


 >It's the big hump that's unacceptable to SMT.

Assemblies with 5000 joints, with alot of devices at 20 mil (thou) pitch,
and significant solder dome height,( we like lots of solder ), present no
problems to us.

Regards

################################################################
TechNet E-Mail Forum provided as a free service by IPC using LISTSERV 1.8c
################################################################
To subscribe/unsubscribe, send a message to [log in to unmask] with following text in the body:
To subscribe:   SUBSCRIBE TechNet <your full name>
To unsubscribe:   SIGNOFF TechNet 
################################################################
Please visit IPC's web site (http://www.ipc.org) "On-Line Services" section for additional information.
For technical support contact Hugo Scaramuzza at [log in to unmask] or 847-509-9700 ext.312
################################################################