i just gave this pcb to a production, it has nrf52840 and pa/lna module, 3v3 LDO on it, practically a stand alone board with nrf52. i did not include a battery connector or charger because its for prototyping. i copied the front end part from my nrf24 modules so if i can solder it should work smoothly. tho this aQFN footprint looks very intimidating 
some of the tracks and gaps are at the manufacturers design capability tolerance limits so lets see if they gonna accept it.
i just received this little thing, tested it with atmel studio just to flash some M4 boards and it worked nicely. i wanted to update its firmware via jlink(playing with fire) but it didnt let me saying its up to date so its all ok i guess. it only has 4 pins 3v, gnd, swdio, swclk. for $2.50 in total with shipping its a steal
@NeverDie soldering bottom/non visible parts needs at least some sort of reflow oven to make sure they melt and make connection. checking for bridges tho is impossible with microscope etc because they are under the chip. diagonal pin pitch is at around 0.55 and the ones on the same row are at 0.5 which is normal qfn package. if you can solder qfn package this is not a problem but the hardest thing is inability of inspection at hobbyist level
aligning is very simple, you just need to have correct courtyard printed on the silk layer of the pcb for the chip/module so when you place the chip/module on to the pcb, it needs to sit exactly on top of the courtyard drawing on the silk layer then you know your pads are exactly where they need to be.
sadly tho bigger parts like these modules cant benefit from the surface tension force is not enough to pull the weight but then again its very hard to misplace them especially the e73 module. raytac modules(blue one in the picture) are hard aswell they are like super tiny heres how it is under the chip but it baked nicely and it works as expected.
i hope to solder aQFN package aswell but im really not sure about that one :)) standard QFN with visible pads on the side is very nice i wish nrf52840 was like that.
@NeverDie price wise i think e73 modules are unbeatable they are 3.. dollar or something with the current discount in aliexpress. just for the nrf52840 Soc price in mouser is $5.5 which is still ok if theres going to be a noticeable difference in signal strength. considering much bigger ground plane and bigger antenna i expect better performance but need to test it aside from the soc theres a low pass filter which is .30 and a crystal which is probably around .20-.30
that blue raytac module was https://www.raytac.com/product/ins.php?index_id=24 8 or $9 which gave almost the same performance as the e73 so at that price point ive not tested it but BT840F($7) looks better and much easier to solder as the bottom pin pitch is whooping 1.5mm or so.. you can park a truck between those pins :))
Today i thoroughly tested nrf52840 modules that i have(2 with ceramic antenna and 2 with ipex connector external antenna) all modules were set to max (+8 dBm) TX power and my observation was kinda disappointing. Setting up services, characteristics etc is fun and all but signal strength is disappointing. I tried ceramic to ceramic, ipex to ipex, ceramic to ipex and ipex to ceramic none of them stood out they gave the same performance. As soon as i put the module in a plastic container or theres more than 1 wall in between packets become unreliable and they just keep dropping, connection slows down etc it just doesnt have enough power whereas nrf24l01 with pa module is rocking even if theres like 10 brick walls in between its not even a competition. I dont think its an antenna problem because it doest get any better than ipex connector so the only option is to add some front end module. There are many options for FEM with different capabilities and functions but I will try to add RFX2401C because im familiar with it and its fairly simple. It is controlled with RX, TX pins but im not really sure how to implement it to a code.
seems like softdevice has a support FEMs but its a question if its gonna work in arduino environment Gotta try and see..
https://devzone.nordicsemi.com/nordic/nordic-blog/b/blog/posts/pa-lna-support-in-s132
also in nordics front page you can see they released a FEM for nrf52 and nrf53's its called nRF21540
quoting from the product page
https://www.nordicsemi.com/News/2019/12/Nordic-samples-nRF21540-RF-Front-End-Module
"The nRF21540 RF Front End Module is a range extender optimized to boost the link budget of Nordic’s nRF52 and nRF53 Series advanced multiprotocol wireless SoCs. When combined with an nRF52 Series SoC, the nRF21540 RF FEM’s +21 dBm TX output power and 13 dB RX gain ensure a superior link budget for up to 16x range extension"
so that kinda proves my point connection is somewhat weak and it needs a FEM any kind to at least bump the power to around 20dBm and it will all be good and usable.
And keep in mind nrf52840 has the most power of all with max +8dBm power, 52832 has 4 and their new workhorse dual processor nrf5340 comes with +3dBm power so probably thats why they are pushing nRF21540 forward to ensure best possible connection.
to reduce evaporation i saw a guy doing the following method. he fills the container with regular water up to middle mark and then gets some fridge ziplock bags fills them with cleaning solution or just IPA puts the pcbs in the bag locks them and tosses bag into the water filled ultrasonic cleaner. when it finished just takes out the pcbs and locks the bags again for later use until the solution or alcohol is not usable. sounds very practical but i dont have experience with it.
hey guys. I'm testing couple of nrf52840 modules. so far i was able to test raytac mdbt50q ipex and e73-2G4M08S1C modules with basic rssi value.
so far ipex version looks abit better but at a cost of external cable and antenna where e73-2G4M08S1C is compact and difference is not that significant.
i later saw fanstel products, particularly interested in BT840F model because reported range is significantly better than the BT840 model and the only difference is the antenna design between them.
Considering this difference 840F might be way better than the e73-2G4M08S1C. Has anyone able to compare them or test them directly?
I also designed this 2 layer breakout board with a much bigger inverted F antenna design for the nrf52840, ive put BT840 to compare the antenna size. (still needs some touch ups here and there)
bottom layer has a good ground layer for the antenna and i believe its going to perform better but just to be sure theres a SMA option for external antenna aswell which can be selected with the 0 ohm resistor.
nordic specialist approved it and i will probably give it a try just to compare the antenna performance. My only concern is how hard soldering is going to be. if you noticed i removed the pins who are next to each other(i left some because they are mandatory like d+ - swclk etc..) and left the diagonal ones in order to reduce the chance of possible solder bridges. as you can see from the picture there are reports about solder bridges detected with expensive xray machines which i dont have so, fewer the pin count less probability for failure.
on the other hand ebyte nrf52840 e73 modules even with the bottom pads are really easy to solder without a probability to bridge anything and cause issues because bottom pad to pad distance is very generous, im really happy with that.
@monte yep, theres a filter cap on my voltage regulator which is picked specifically because of its very low noise performance and the modules have filter caps as well not only 1 but 3. oh also worth mentioning, i designed nrf24 modules with pa lna to compare the performance and used fancy baluns and RF filter components with proper sma antenna and to be honest performance difference was unsignificant for much more work and more costly. balun is .80 , band pass filter is .70 original nrf24 chip is 3 and pa module is 2 crystal, connector other passive components all add up to around 7-8 dollars which gives similar performance to E01-ML01SP2 at only 2 dollars.
edit: as for the issues with E01-ML01SP4 i know its a grounding issue but its very hard to pin point the cause. i pulled my hair out many times :)) i just blame the tiny ipex connector or just the bad antenna.. somewhere along the line grounding was the issue but none of these antenna related issues happened with my own nrf24 design or the E01-ML01SP2 so its definitely either connector or antenna issue. good old solid as a rock SMA connector is the best if it is not available i would go with pcb trace or ceramic antenna.
@NeverDie Well BT840X has built in FEM SKY66112 if im not mistaken, thats why you are getting good results but how did you make it work in the code. Because for TX and RX you need to tell the NRF when to listen and when to transmit so the FEM can flip switches inside and work its magic.
Tomorrow i will try a remote application where client transmits analog read data every 50ms and reports it to the peripheral device, i will put it in a plastic box and wrap my hand around it and see how many packets it will drop tho im really skeptical after today.
@scalz thanks for the input, ive seen they tune it by cutting a length from the longer end but in order to do that i need equipment which i dont have so its going to be a hit or miss if it doesnt work well i can use SMA antenna but i think thats the least of my worries with that pcb. I like to experiment and see for myself so even if its wasted its ok
@Mishka i was looking at that long range support of nrf52840 by lowering the data rate to 500kbps or 125 kbps you gain a significant amount of range like 4 fold but it requires a coded PHY which is not available in arduino environment at least not that i know of. adafruit marked it in their to do list but know knows when they gonna implement it probably thats why nrf24's make a significant difference in signal strength when you lower the data rate to 250kbps.
Yes that amplifier draws quite abit of current i think it was up to 350ma when tx is on but ofc it is not on all the time so but still its not for everyone.
i will look into that antenna you mentioned while im waiting for the pcbs thank you for the suggestion!
antenna that i used in the pcb is this one: i read its better than chip antennas but ofc at a much bigger footprint
http://www.ti.com/lit/an/swru120d/swru120d.pdf
usb connector is actually nested as far as i can see but it dips 1-2 mm only. weird but it works so its all good
to reduce evaporation i saw a guy doing the following method. he fills the container with regular water up to middle mark and then gets some fridge ziplock bags fills them with cleaning solution or just IPA puts the pcbs in the bag locks them and tosses bag into the water filled ultrasonic cleaner. when it finished just takes out the pcbs and locks the bags again for later use until the solution or alcohol is not usable. sounds very practical but i dont have experience with it.
i just received this little thing, tested it with atmel studio just to flash some M4 boards and it worked nicely. i wanted to update its firmware via jlink(playing with fire) but it didnt let me saying its up to date so its all ok i guess. it only has 4 pins 3v, gnd, swdio, swclk. for $2.50 in total with shipping its a steal
@Jon-Raymond exactly too much in the middle will raise it and bam you have a failed board
@Mishka its a wise choice to ask for assembly because of the reasons you mentioned. ENIG is kinda mentioned everywhere for this aQFN footprint otherwise surface might not be even for every single pin and it will result in failed soldering BUT i still went with HASL just to prove them wrong :))
capped via service is expensive so i just went through every single pin to examine and decide if i really need it or is it necessary for it to work and spaced them out as much as i can. i still got plenty, 3 analog pins, 9 high speed digital pins and rest is low frequency pins which are not recommended for high speed operations. it can interfere with the bluetooth signal. nordic specialist approved the design so if everything goes well it should work.
my only worry was the at the bottom side XC1 XC2 pins you can see they are really close to each other i think it was 5 mil but still it was in the capabilities so it went through. i ll see how it goes its gonna be interesting.
and yes i use stencil and a reflow oven.
how do you like the antenna performance of the nrf52840? sadly it doesnt meet my requirements so im trying this pa lna method to see if i can make it work.
@Calvin-Khung Well im actually surprised that it still works because people are reporting they might stop working after a firmware update so you might wanna hold back on that other than that it works surprisingly well. i bought another as my back up plan which im expecting it in these days. its abit different than the one i have. this one is much cheaper and looks like jlink edu mini rather than a normal j link with a black box.. i ll see if it works when i receive it, here it is.
https://www.aliexpress.com/item/32669702891.html?spm=a2g0s.9042311.0.0.27424c4d4Fx7g9
i just gave this pcb to a production, it has nrf52840 and pa/lna module, 3v3 LDO on it, practically a stand alone board with nrf52. i did not include a battery connector or charger because its for prototyping. i copied the front end part from my nrf24 modules so if i can solder it should work smoothly. tho this aQFN footprint looks very intimidating some of the tracks and gaps are at the manufacturers design capability tolerance limits so lets see if they gonna accept it.
i use $10 replica Jlink from aliexpress works ok with the latest firmware without an issue. i use it just to flash bootloaders to cortex m0-m4 and nrf52's but it should work for any task that a genuine jlink can do.
@Jon-Raymond selling them was not my intention but i have around 8 bare pcbs and 2 built ones. i can fix you up with one of those if you want to or i can cook totally brand new one up to you.
