Not-too-yellow FR4 material for PCBs? - Page 1
Forum section: electronics / general

author: ebastler
author_rank: Super Contributor
timestamp: August 31, 2017, 02:23:50 pm
content: I have a project where I designed the front panel from PCB material, and played a bit with solder mask, tinned areas (HASL), and exposed bare PCB material to mimic the look of a vintage computer's control panel. I am quite happy with the way it looks, with one exception:The areas to the left and right of the main keypad were originally made from whitish, translucent plastic (acrylic?). I try to approximate this look with the exposed bare PCB material. But the FR4 boards I have received from various suppliers so far are all distinctly yellow -- which does not look right, and in fact looks a bit unhealthy.Is anybody aware of flavors of FR-4 (copper-clad, for use in PCB production) which are essentially white? Any recommendations for PCB houses which can supply and work with such material?Thanks!

author: tszaboo
author_rank: Super Contributor
timestamp: August 31, 2017, 03:07:43 pm
content: I think the type of epoxy makes the FR4 inherently yellow. You can print silkscreen over it, and then it is white. Or use CEM1 as base material, but I doubt anyone offers pooling on that terrible material.

author: ebastler
author_rank: Super Contributor
timestamp: August 31, 2017, 06:12:06 pm
content: Thanks, NANDBlog. You might be right there, but I am not giving up hope yet..FR-4 seems to be the designation for a broader class of epoxy & fiberglass plates. I have certainly found FR-4 which looks essentially white (but is not copper-clad), e.g. here:http://www.masterplatex.de/Type-FR4-white.But of course it is quite possible that the FR-4 variety used for PCBs is always made with yellowish epoxy. I can certainly see that for more typical use cases one couldn't care less about the color!I have considered using white silkscreen on that surface, but would like to avoid it. The flat-white look is not what I'm shooting for; I would prefer the slightly "deep", milky appearance of bare epoxy board. And the silkscreen layer would hide the nice subtle logo, which uses thin copper traces.Still hoping that someone has come across white FR4!

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: August 31, 2017, 07:17:06 pm
content: You can get coloured FR4 - it's just a case of dye being added to the resin, however it would be a special order with significant minimum order qty and leadtime.

author: schmitt trigger
author_rank: Super Contributor
timestamp: August 31, 2017, 07:40:05 pm
content: Beautiful project!I was also going to suggest CEM-1.

author: Fred27
author_rank: Unknown
timestamp: September 01, 2017, 08:47:48 am
content: I got some blue FR4 from a UK supplier - thinking they were presensitised boards with the blue protective covering. If that's any use let me know and I'll dig out the details (or perhaps even the unused boards).

author: cdev
author_rank: Super Contributor
timestamp: September 01, 2017, 11:43:22 pm
content: Yes, and I was surprised torecently read this.."Why are we using the White PCB?Many curious people have asked me such question (PS: we did not kill any cat yet). This is always a little secret of VoCore, but today I will talk. It is not only about its looks better, also it is part of quality control.PCB mainly has six colors, green, blue, red, yellow, white, black. (the truth is you can choose any RGB 24bits color you like, somebody even choose purple)Most of the factories love black and green, that is because the first pass yield around 95% ~ 98%, the not good ones will send back to workers and repair, during the repairing, the pcb boards have to be heated to 260C again, green and black pcb is good but white pcb will change to light yellow one.Most repaired ones are good, but the quality might come low. Sn after heat and heat again will partly become SnO2, SnO2 is not conductor and have a high chance broken the connection.So we decide we only ship the first pass VoCore to users, and use white PCB to make it easy to check every VoCore we shipped is first class quality.PS: another fact is I am lazy, keep them 100% good rate so I can have more time on bed but not shipping the packages again and again. :p"

author: EEVblog
author_rank: Unknown
timestamp: September 02, 2017, 01:27:54 am
content: Quote from: ebastler on August 31, 2017, 02:23:50 pmNever heard of anyone carrying coloured FR4 core as stock, there is just no industry need for it.If youreallyneeded it then if would be possible to find a supplier, but you'd be hit with a minimum order of panels no doubt. And that'sfullpanels.

author: Yellofriend
author_rank: Regular Contributor
timestamp: September 09, 2017, 02:43:42 pm
content: In the ol' days all FR4 was sort of of whitish opaque translucent. Then some multilayer PCB makers wanted a material that blocks UV light - that is the yellow translucent FR4 you see often nowadays. They simply mix a light wave blocker in the epoxy that blocks UV.You can still ask for FR4 without UV blocker, it's still produced.CEM-1 is a paper material with epoxy as binder (FR1/FR2/XPC use a phenolic binder) - plus one layer 7628 (200g/m²) glass fabric (as prepegs) on top and bottom (1.55mm FR4 uses 8 layers of 7628 prepregs) and not suitable for chemical through hole. Silver or carbon paste through hole can do. CEM-1 is naturally slight yellowish, but often they add TiO2 to the epoxy to make it white.Colored FR4 is possible but very rare. They have to clean the treater for ages after each lot. Should be quite hard to find.

author: radar_macgyver
author_rank: Frequent Contributor
timestamp: September 09, 2017, 07:15:28 pm
content: If you can eat the cost, use Rogers 4350, it is a pure white (but expensive) substrate. Prepreg thickness is low, but you could find a multilayer stackup with FR4 to make it rigid.Quote from: Yellofriend on September 09, 2017, 02:43:42 pmInteresting. Also, is that username just a coincidence?

author: cdev
author_rank: Super Contributor
timestamp: September 09, 2017, 08:21:42 pm
content: The quote wasn't me. I was quoting from the Vocore web site. Vocore is a very tiny approximately 1 inch white PCB with a wireless AP on it, that can also run Linux (via openwrt) apps.. Its white. The quoted text was vonger,the board's maker's opinion.I was posting it because indeed, its a tiny white PCB, and the quote was vonger's argument why he used white and not green, or whatever.He is Chinese and he makes his boards in China. I don't know any more than what's on his site.Quote from: blueskull on 2017-09-01, 18:31:06>Quote from: cdev on 2017-09-01, 17:43:22>Most repaired ones are good, but the quality might come low. Sn after heat and heat again will partly become SnO2, SnO2 is not conductor and have a high chance broken the connection.This is. For most consumer gears operating at room temperature (not including those CPUs thermal cycling from room temp to 100C 1000 times per day), solder joint isn't a significant failure mode at all.Also, tin oxide will not form at any significant quantity at common solder temperature, and even there are some, most are reduced by flux. The remaining will be expelled to sides of the solder joint by surface tension of molten solder.Most chips are rated for twice or 3 times of reflow while still have industrial or even mil standard quality, thus allowing at least 1 time of reworking.The reason people don't want to reflow the PCB for so many times is because:1. This process wobbles the PCB, so chips aren't sitting in a perfect plane anymore, inducing failure.2. Hot solder dissolves pad metal, and the dissolved metal makes solder less eutectic and more brittle.3. Reworking (partial refow) induces stress on large parts which have half balls/pins reflown while half not.4. Reworking heats adjacent parts, if they are not protected by flux, oxidation may occur, semi-conductive tin oxide may short pads.5. Reflowing without adding new solder and wicking old solder causes dissolved gold plating to form more complicated IMC, which are brittle.Knowing what to do and understanding the physics of soldering, these problems can be prevented. For instance:1. PCB wobbling can be avoided by using high Tg material and using a slower temperature profile (eg, using a preheater instead of nuke the board just with hot air).2. Using properly made ENIG surface (with relatively thick Ni layer with correct portion of P), OSP or HASL, instead of crappy quality ENIG, use consistent solder type.3. Cover nonintended large chips with Kapton film or aluminum foil.4. Generously apply flux and get a decent ultrasonic cleaner to remove them later.5. Always clean up pads and apply fresh solder after removing a chip. If change of solder is necessary, then tin and wick multiple times to make sure old solder is completely removed from both pads and iron.

author: Yellofriend
author_rank: Regular Contributor
timestamp: September 10, 2017, 02:27:43 am
content: Quote from: radar_macgyver on September 09, 2017, 07:15:28 pmYes a coincidence. I do work with laminates though. Here and then I get request for non-UV type FR4, usually for application that are not really PCB related were they need a UV light pass through.Quote from: cdev on September 09, 2017, 08:21:42 pmThat is most likely standard FR4 with a white solder mask.People often confuse the color of the laminate with the color of the solder mask. After solder mask it's near impossible to tell the color of the laminate. However, you can check if it has UV blocker in it or not by using a UV flashlight/torch on the edges. Laminate with UV blocker has a strong fluorescent reflection under UV light.

author: Cerebus
author_rank: Super Contributor
timestamp: September 10, 2017, 08:12:51 pm
content: Quote from: blueskull on September 02, 2017, 12:31:06 amJust a pedantic point about this, something can't be "less eutectic", it either is a eutectic or it isn't. The eutectic point is just that, a point on a material's phase diagram.Thank you for paying attention, this has been today's pointlessly pedantic fact brought to you by a man who used to share a flat with a metallurgist who went on and on and on about both eutectics and stress corrosion cracking. Your indulgence has been appreciated.

author: wraper
author_rank: Unknown
timestamp: September 10, 2017, 08:36:39 pm
content: Why would you care about FR-4 color at all? Just order PCB with white solder resist.

author: ebastler
author_rank: Super Contributor
timestamp: September 11, 2017, 11:11:14 am
content: Quote from: wraper on September 10, 2017, 08:36:39 pmReading my initial post above might help to clarify. A rather niche requirement, I admit. ;-)

author: tooki
author_rank: Super Contributor
timestamp: September 19, 2017, 03:51:56 am
content: Didn't Bigclive have a big stash of white PCB that he used? But I think he mentioned it being discontinued now.However, isn't the aluminum-backed PCB material intended for LED lighting applications white? It might work well for this application.