My initial instinctive response would be that HASL would normally give a sufficiently long shelf life. Also that overall HASL (properly done) gives the least solderability issues. Therefore a change from HASL probably would not address their quality issues. Of course they might have unreasonable concept of storage time. How long is a long time for them? Or they could have had a batch of PCB with improperly applied HASL, For example the solder layer was levelled too thin, leading [in storage] to the coating being all unsolderable intermetallics. On an ENIG board the Au layer is very thin and although intermetallic layers do not tend to form between the Au and Ni, the Ni can oxidise below the very thin layer (<0.0X um) of Au and become hard to solder. In either case we should be talking long times here, up to years. So very possibly their conditions of storage/packaging or time expectations are the issue not type of finish. (Assuming this is not a one off batch related issue). When hand soldering you need to think of the heat input and not just temperature. If you reduce tip temperature you will increase time to solder. The thermal burden can therefore be more not less. You need a hand soldering specialist to answer this better, But a Sn/Pb with MP of 183 needs a superheat to a min 210C preferably 220C to work. With a tip temp of 210 you will be effectively waiting for the work to come to equilibrium with the soldering iron, and will still not be hot enough. Solder flows to wards heat and onto solderable surfaces. If the component leads are less massive than the circuit they will heat first. And solder goes there. If you have pad solderability issues then that will not help. Possibility a change in technique is required, but certainly a higher tip temperature than 210. I would guess a min 250C, maybe 260 depending on the quality of the iron temperature control. Tip shape is also important in determining effective heat transfer and flow. Regards Mike -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Uppina Nagaraj Sent: Thursday, June 17, 2010 12:30 PM To: [log in to unmask] Subject: [TN] Query on shelf life of PCBs & impact on solderability Dear All, I have 3 queries in all..... 1. One of our customer has changed the surface finish from HASL to ENIG. Their main reason for this change was that they have had a bad experience with storage of HASL finished boards (the reason for which is not shared with us). They had encountered solderability problems on the HASL finished board which they had stored for a period of time. Their expectation with Gold plated surface is the storage of the PCBs can be for a longer period of time as compared to HASL finish. Initially they had a requirement for 1micron thick electrolytic gold, but later on they changed the requirement for an ENIG process with gold around 0.05 to 0.10 microns. Now my question...... Is there any guideline on the shelf life of the PCBs (with regard to solderability) of the following surface finishes.... a) ENIG b) HASL c) Immersion Tin d) Electrolytic Ni and electrolytic gold with Gold thickness of 1.0microns Will vacuum packing help to extend the shelf life? 2. One of our customer is doing hand soldering of PCBs with ENIG finish. They're inserting a strand of tinned Copper wires from component side and later on using soldering iron to do the soldering from the solder side. The solder is able to flow up from solder side to component side, but the solder is unable to complete wet the pad on the component side. I've attached the photos of example of the phenomenon. These photos are without the wire, I've just used bare PCBs to do the soldering to illustrate the phenomenon. Now my question.... a) Will increasing the volume of the solder help in complete wetting of the pads on the component side? b) Any other way to get a full coverage on the pads on the component side. 3. This question is about the same customer which I've mentioned in para 2 above, is doing hand soldering. In one of the stage of component assembly, they're (hand) soldering a flexible PCB on the ENIG finished rigid PCBs. They have a unique practice during this stage of soldering. They've explained to us that this particular component is very sensitive to high temperature and hence the soldering iron temperature is set at 210Deg C. They're using Sn60/Pb40 solder for this soldering operation. After the soldering iron achieves 210Deg C, they're turning off the power to the soldering iron and doing the soldering of the flexi PCB onto the rigi PCBs. We'll not know the actual soldering iron temperature at the point of contact. They've complained to us that the soldering is poor. We know that the melting temperature of solder is around 183deg C. But, is there any guideline on the minimum temperature for soldering to get a good flow of solder and completely wetted solder? Thanks for your inputs in advance. Best Regards, U.Nagaraj MICROPACK Ltd, Bangalore, INDIA. ______________________________________________________________________ This email has been scanned by the MessageLabs Email Security System. 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