| | We have a product, with various PWBs, with over 600 parts each one (We are a low Volume/high mix company with an average component placement per PCB between 250 to 300 parts). This PWBs have 7 to 10, 20 mils pitch parts. We are having problems with our raw edge supplier because we specify 200 to 400 microinches and he can not achive it on his normal process, they are always very low below the lower limit. This PWBs are Hasl finished. | | | | When is the time to change to an alterantive plating finishing ? 20 mils ? 15 mils ? | | | | The supplier recommend Omikron. I already read notes about omikron suggestion. OSP ? Any suggestion ? | | | | Thanks, | | Jose RG | | | The other options, like HASL, all have their ad- and disad-vantages. I like OSL, but this limits the range of fluxes/pastes you can use for best results. Au/Ni can cause solderability problems, as the Au dissolves instantaneously in molten solder (forming intermetallics which may weaken the joint - see Manko or Klein Wassink) and the underlay of Ni must be oxide-free when gold plating starts and the Au must not be significantly porous to prevent re-oxidation. Oxidised nickel is hell to solder unless you use a strongish hydrochloride-activated flux (again, see M or KW). | | Brian | Brian says the right things, but remember not to be too tight with your HASL specification, if you use one at all. It's just not possible to specify thickness requirements - min or max.
Also, adding to what Brian said, nickel simply is a barrier between copper and gold - nothing more. I certainly agree about nickel oxidation being a problem. It oxidizes very rapidly and can be difficult to control in the immersion deposition process.
Another hot element, though it seems few are listening but the "big" guys (Motorola, GM, H-P, etc.) is the negative impact phosphorous has in the equation. These folks have really put a damper on any type gold. Phosphorous is an essential part of the nickel deposition process and it causes solder joint failures as embrittlement,while having been found to contribute to the now notorious "dark gold" phenomonon, not always the gold - in minimal thicknesses (3-7 u"). The same possibly would be said if a supplier substituted boron, as an example, for phosphorous.
Earl Moon
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