Resistance of ENIG vs. HASL - Page 1
Forum section: electronics / projects

author: ROBOT
author_rank: Contributor
timestamp: March 25, 2016, 09:01:02 pm
content: I did a quick search but could not find any articles about a clear resistance advantage over ENIG.Just to throw this out there:Nickel is 6.99×10-8 (?·m) at 20 °CGold is 2.44×10?8 (?·m) at 20 °CNow the killer Lead free HASL is mostly tin!Tin is 1.09×10?7 (?·m) at 20 °CNow an ever bigger killer for all you lead solder lovers!Lead is 2.20×10?7 (?·m) at 20 °CPlease debate over why this should be taken into account or completely ignored.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: March 25, 2016, 09:52:45 pm
content: The gold layer on ENIG is so thin that I doubt it makes much difference.

author: m98
author_rank: Frequent Contributor
timestamp: March 25, 2016, 10:01:25 pm
content: Never thought about it, but according to your numbers ENIG has a smaller resistance than HASL. How would it matter? I don't think that there's any relevant resistance difference between a solder joint on an ENIG pad and an HASL pad.

author: nukie
author_rank: Frequent Contributor
timestamp: March 25, 2016, 10:51:33 pm
content: I read from somewhere gold actually resolve into the solder.

author: KL27x
author_rank: Super Contributor
timestamp: March 25, 2016, 11:04:46 pm
content: QuoteThe traces connect two components. And those components have leads. Or in the case of BGA those leads are pretty short, but they are floating through a solder layer.So calculate the conductivity of your components leads and then get back to us.If a layer of gold a few molecules thick will make any difference, I will be surprised.If you're talking about the increased conductivity of the trace, itself, the resistance of the trace can be economically reduced by making the traced thicker and/or wider. Ask your manufacturer the price of increasing the thickness of your ENIG.

author: ROBOT
author_rank: Contributor
timestamp: March 26, 2016, 12:09:59 am
content: Quote from: KL27x on March 25, 2016, 11:04:46 pmIt's actually not the gold it's more like the nickel is better than the tin. Sure the gold layer is super thin but the nickel is much much thicker than the gold.Sure it might not matter. But I wonder if any applications actually consider this. Maybe some high frequency stuff?

author: KL27x
author_rank: Super Contributor
timestamp: March 26, 2016, 09:00:12 pm
content: The nickel and gold are both (I am betting, since component leads are magnetic) much better conductors than a component lead, so it doesn't matter how thick a plating of gold/nickel there is, or if it's not there at all. If you were inserting a significantly higher resistance surface layer between the component lead and the trace, then you might care how thick it is. Right? What am I missing?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: March 27, 2016, 06:21:58 am
content: (At least with reputable manufacturers,) you start with copper foil of a certain thickness, usually 1/2 or 1 oz.Copper is then plated on top, masked, and the rest etched away.At the point you have the nominal 1 or 2 oz. or whatever.Any plating on top of that can only reduce resistance further. It doesn't matter if it's tin or lead or anything else.But the plating depth is very shallow, in the microns. So it doesn't matter that gold is used, whether or not it dissolves (which it does*), it's too thin to matter.*The gold flash is mainly a means of soldering to nickel. The gold tins easily and prevents the nickel from oxidizing, whereas bare nickel forms an oxide layer that's difficult to solder to. Once the joint is formed, it goes copper-nickel-solder, with no evidence of gold remaining.So if you want reduced resistance, increase the copper foil thickness, or add big gobs of solder along the tracks. "Plating" the tracks with wave solder blobs will do far more than all types of thin surface platings.Quote from: evb149 on March 26, 2016, 11:33:23 pmThe distribution is quite easy to spot, once you know what to look for.At high frequencies, current follows the path of least impedance. This is along a trace, and in the accompanying ground plane along the same path. (If you don't have a contiguous ground plane, guess where it has to flow instead...)Current concentrates between facing sides of parallel plates, along edges of plates (another skin effect), and around inside corners of bends. Likewise, the image current (in the ground plane) is higher in the same locations, diffused a bit by distance. (This is only noticeable when the trace-to-plane spacing is comparable or shorter than the trace width.)At RF, the EM energy doesn't travel inside the wires or traces: indeed, fields are excluded from the bulk of conductors, because of their conductivity (skin effect). Conductors provide a path for the field to travelbetween. Losses are dominated by PCB material (where the electric field dwells) and surface conductivity (where the magnetic field is reflected from).The outer-surface plating of a PCB has almost no effect on losses, because of course, almost no current flows there! The inner surface (facing the laminate) is important. Where RF losses are critical, this should be smooth bare copper; traditional PCBs use etched oxide copper, which gives a better grip to FR4. (Rogers or similar laminates give a poorer grip already, so you can imagine the traces are somewhat fragile in a circuit that needs low losses on all of these structures.)The electric field still flows through the air. Indeed, a microstrip trace has a hybrid dielectric with air, which means the field "on top" travels at light speed, while that inside the PCB travels slower (\$\sqrt{\epsilon_r}\$ times slower), leading to dispersion (a difference in propagation velocity versus frequency; square waves get somewhat rounded off). Any lossy materials in this space will contribute to overall losses, which is why RF circuits typically omit solder mask around important traces.QuoteYup. A chip component, for example, will have the current flowing along the bottom face of the trace, then up around the edge of the pad, into the component termination, and across its structure (which will be pretty meaty for a chip capacitor, or elevated on the alumina substrate for a chip resistor*).*You can flip resistors upside down to get slightly better VSWR in the >10GHz range. This only matters on resistor values very close to Zo (50-150 ohms for most PCB traces), as other values naturally look inductive or capacitive anyway.QuoteHASL is done with SMOBC (solder mask over bare copper). In prior days, the board was left with tin plate (from a prior etch-resist step), which tended to wick solder during reflow, leading to wrinkled soldermask:http://www.mtarr.co.uk/courses/ami4945_dpb/u01/supplementary/sup_01.htmlThe extra meat would tend to reduce resistance, though!ENIG can be done before or after soldermask; usually after, but there have been examples of boards plated either way.Tim

author: radar_macgyver
author_rank: Frequent Contributor
timestamp: March 27, 2016, 06:37:21 am
content: Here's a link with a focus on microwave boards:https://www.rogerscorp.com/documents/2341/acm/articles/Ambiguous-Influences-Affecting-Insertion-Loss-of-Microwave-Printed-Circuit-Boards.pdfThe added losses are very small under 10 GHz.

author: calexanian
author_rank: Super Contributor
timestamp: March 28, 2016, 02:36:30 am
content: HASL in the most dependable for reflow. It actually is the easiest to flow for any process including hand. Gold flash (Which is really all you get. Nobody really plates anymore) causes more problems than it solves as its solderability is low. You have to wait for it to actually alloy with the tin. very time consuming with no clean flux and lead free solder.

author: IconicPCB
author_rank: Super Contributor
timestamp: March 28, 2016, 07:32:26 am
content: Tim,Please expand on flipping resistors.. is a better VSWR achieved and why why ?Proximity of conductive layer to ground plane in the body of the chip?

author: IconicPCB
author_rank: Super Contributor
timestamp: March 28, 2016, 01:04:32 pm
content: HASL is done with any type of solder...ENIG and other forms of gold plating may create a problem for a PCB shop since often the plating is performed in acid based Cyanide process.Immersion silver ( silver over copper) is based on a detergent chemistry.ENIG is often offered as solderability layer which also offers the flatter surface for fine pitch SMD designs.Silver offers the same planarity as does ENIG minus the nasty chemicals.

author: G0HZU
author_rank: Super Contributor
timestamp: March 28, 2016, 01:54:42 pm
content: I've had problems with ENIG when used up in the GHz region, especially when used in printed (narrowband) bandpass filters. It can be very lossy. A prototype filter up at maybe 2GHz milled with copper can have a much lower insertion loss than the same filter using ENIG plating on a mass produced board from a PCB manufacturer using the same PCB material (eg Rogers 4003C).

author: ruffy91
author_rank: Regular Contributor
timestamp: March 28, 2016, 02:11:08 pm
content: Isn't the problem why you would choose ENIG over HASL that you can solder with any alloy to it, in contrast to HASL where you have to get an alloy which is compatible to your pcb manufacturers HASL alloy? (Plus the planarity issue for BGAs and small pitch components)

author: calexanian
author_rank: Super Contributor
timestamp: March 28, 2016, 05:08:04 pm
content: Tin dip plate is common at the cheapest places.

author: IconicPCB
author_rank: Super Contributor
timestamp: March 28, 2016, 09:18:12 pm
content: I would not use FR4 for anything over a GHz... especially not RF filter structures whihc might require high Q elements.FR4 is lossy and non uniform ( due to fibreglass matting) in 3D.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: March 29, 2016, 08:11:00 am
content: Quote from: IconicPCB on March 28, 2016, 07:32:26 amYes. The resistive layer is on the top.This is only of any significance at wavelengths on the order of the resistor body, and really should be considered a component size or value error. Don't actually make production flip over the resistors...Tim