hey guys, i finally assembled my nrf52840 pa board. it was sitting there for quite some time but i couldn't find some spare time to get on with it but here are some experiences i had.
i was worried about this aQFN footprint but it all went well, looks like everything is soldered correctly and i ordered my boards with cheapest HASL instead of ENIG.

then i uploaded the adafruit feather bootloader to test the bluetooth and it all works ok. i used my iphone 6s as a central device and im not sure if my phone has LNA or PA module inside for bluetooth so it may or may not be better if i use another module like the one i did. this connection is from my module to my phone WITHOUT PA activated at tx power max(8):

and this is after i activate PA chip on board :

and this is with 3 solid walls in between at around 10 meters distance

as you can see signal strength is massively different pa bumps up the signal from -87dbm to -30dbm which is probably day and night difference.
but with this setup you manually have to enable and disable rx and tx pins in order to keep the communication. well im not really good at coding but im going to try make the whole thing automatically because nordic already has this PA assist feature buried inside its BLE core, just gotta find a way to make it work.

final board, forgot to add i opted to use pcb antenna but i could switch to external antenna as well i just have to reposition the 0 ohm resistor to use that SMA on the side and then results could get even better:

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

after abit of looking around and testing i think i made it work at least examples are quite responsive without a single disconnect. i had to add some header files and extra bit of code to every sketch so the knows how to use PA/LNA.

static void pa_lna_assist(uint32_t gpio_pa_pin, uint32_t gpio_lna_pin)
{
    ret_code_t err_code;

    static const uint32_t gpio_toggle_ch = 0;
    static const uint32_t ppi_set_ch = 0;
    static const uint32_t ppi_clr_ch = 1;
    
    // Configure SoftDevice PA/LNA assist
    ble_opt_t opt;
    memset(&opt, 0, sizeof(ble_opt_t));
    // Common PA/LNA config
    opt.common_opt.pa_lna.gpiote_ch_id  = gpio_toggle_ch;        // GPIOTE channel
    opt.common_opt.pa_lna.ppi_ch_id_clr = ppi_clr_ch;            // PPI channel for pin clearing
    opt.common_opt.pa_lna.ppi_ch_id_set = ppi_set_ch;            // PPI channel for pin setting
    // PA config
    opt.common_opt.pa_lna.pa_cfg.active_high = 1;                // Set the pin to be active high
    opt.common_opt.pa_lna.pa_cfg.enable      = 1;                // Enable toggling
    opt.common_opt.pa_lna.pa_cfg.gpio_pin    = gpio_pa_pin;      // The GPIO pin to toggle
  
    // LNA config
    opt.common_opt.pa_lna.lna_cfg.active_high  = 1;              // Set the pin to be active high
    opt.common_opt.pa_lna.lna_cfg.enable       = 1;              // Enable toggling
    opt.common_opt.pa_lna.lna_cfg.gpio_pin     = gpio_lna_pin;   // The GPIO pin to toggle

    err_code = sd_ble_opt_set(BLE_COMMON_OPT_PA_LNA, &opt);
    
}

in this form i like the ble, without pa not so much. theres just big down side which is nrf52840 definitely not hobbyist friendly. next time i may design a quick nrf52832 pa board (this one has regular QFN package) to test with the same setup and compare the results.

I recently bought an ultrasonic cleaner and i was looking for a cleaner solution and i made some tests heres my experience;
ive tried everything from IPA to acetone with a stiff/soft brush and it just does not deliver that squeaky clean appearance. Then i tried water based pcb cleaner this one (https://termopasty.pl/en/produkty/water-pcb-cleaner)and it is acutally worse than ipa or acetone.
Then i bought an ultrasonic cleaner and started experimenting at 60C heated solution. My setup is just plain tap water to just below max liquid line and then i get a ziplock bag and put my cleaning solution inside around 100-150ml very small amount and then tossing a pcb inside the same bag. then i put the bag inside the ultrasonic cleaner. this way i can get away with very small amount of cleaning solution and save it for later in the same ziplock bag. So far it works i would say as good as a professional looking PCB but there are some caveats. I tried IPA, Acetone, Ethanol and water based PCB cleaner solution(the one i linked above) all in separate occasions to test them individually.
1- IPA(%99) and Ethanol(%90) works equally well final product is squeaky clean after 3 mins. which i could not get the same result with just a brush. its not even close, im not sure if it is the ultrasonic action or 60C heat but theres a day and night difference between brushing and ultrasonic method.
2-%100 Acetone, this one was an experience at 60C ziplock bag started to expand because acetone started to boil. this boiling action did not happen with IPA or ethanol. Final result was again squeaky clean and it did not melt anything it didnt even remove silk screen. my pcb has 0603 parts qfns and tqfp packages. didnt have plastic switches or connectors unless im out of IPA or Ethanol i would not use acetone not because its harmful for the pcb but it is scary to work with. I will probably gonna make one more try with room temp water and see the result of cleaning. Because that boiling and expansion was scary.
3-Water based PCB cleaner made a huge gummy mess it made it worse than before so i dont know i was so disappointed because its the most safe solution to work with but NO! simple as that.
4-Soapy water with purified water again it did not make any effect even after 6 mins it was the same.

So bottom line in my experience IPA or Ethanol is the way to go. i only wonder if heat is the key thing here or the combination of ultrasonic +ipa. for that my next try will be the same setup but without heat to identify which has the key role in this awesome result.
this image was taken after 5 minutes brush with IPA+acetone:

And this is the same board after only 3 minutes in ultrasonic cleaner in IPA:

@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.

@NeverDie i had to use stencil because i cant inspect aQFN soc from outside. as you can see every pin is at the bottom of it and they are very tiny. to make sure theres correct amount theres no other way than using stencil. to be honest i was expecting problems but it was ok

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.

@NeverDie the ethanol i bought from the pharmacy was very cheap 150ml bottle on the label it says it is for disinfection the skin like before penetration of needle etc its for medical use but what matters is its %90 the rest is clean water it says on the label.
theres absolutely no oily or stick residue otherwise i wouldnt have used it. I did like 10 boards 2-3 with IPA, ethanol, acetone and water based solution while testing.
I watched quite abit of videos in youtube most of the people dunk the pcb in clean deionised water as a final wash to eliminate any left residue. Unfortunately i dont have it but i will buy some soon and i will do the same but for now no residue at all.
wow! denatured alcohol is so cheap over there. i would have definitely tried it i mean if it works it works.. just need to test it with some scrap pcb but on the other hand you are right about the handling it. it might be toxic especially if theres methyl alcohol in it but the one i got supposed to be used on human skin so i believe its completely safe. Safest bet is probably IPA and with the plastic bag method you really minimize the evaporation and amount used so it should last for quite some time. its just good practice to put it back into its bottle(different one ofc). today i noticed a small leak in my plastic bag so its not a good place to store the IPA.

@NeverDie the one in the picture is actually just mechanic solder paste. the reason it looks so messy is when it dries up i mix up some extra flux to the solder paste container to make it shiny and spreadable and result looks horrible after the reflow otherwise when its fresh and new it looks awesome and i believe you can get away without any cleaning. as an extra flux im using nc559 asm but i think its not genuine but works really nice for rework.
the bag im using is this one https://www.ikea.com/ca/en/p/istad-resealable-bag-red-20339284/ no damage at all but i decided to dump the used IPA or Ethanol to a small PP bottle(they are very common) using a funnel to minimize the evaporation. so far my 150ml ethanol looks dirty but so far i used it 10 times and cleans awesome.
And for the record i did that test i mean i didnt use any heating and result was the same so i believe its not the heat but the ultrasonic action combining with the IPA or ethanol is the magic.
Like i said acetone is just too dangerous for us to work with. when i was dealing with acetone i had to take everything outside because i dont have a good ventilation inside and if you inhale even for a second your body tells you hey you need to know its dangerous wheras IPA or Ethanol is so easy to work with.

edit: ikea says they are made of Polyethylene

@Nca78 i dont have a hot plate otherwise i would have tried it. i have soft and stiff bristle antistatic brushes i tried everything to make them look nice and clean but somehow it doesnt work, i was really frustrated. may be for bigger IC packages brusing with ipa might work but for smaller ICs like 0.50mm pin pitch brushing does absolutely nothing. I believe the gaps where needs to be cleaned are too small for a brush to do its job.

%90 ethanol is cheap can be bought from pharmacy ipa depends on the supplier it is cheap too but im absolutely %100 satisfied with the result. probably its a good idea to give them one final wash with a deionised water to remove any residue left from the dirty IPA or ethanol. let the boards sit for couple of days or bake them in the oven at 80-90C for half an hour and its done.

I recently bought an ultrasonic cleaner and i was looking for a cleaner solution and i made some tests heres my experience;
ive tried everything from IPA to acetone with a stiff/soft brush and it just does not deliver that squeaky clean appearance. Then i tried water based pcb cleaner this one (https://termopasty.pl/en/produkty/water-pcb-cleaner)and it is acutally worse than ipa or acetone.
Then i bought an ultrasonic cleaner and started experimenting at 60C heated solution. My setup is just plain tap water to just below max liquid line and then i get a ziplock bag and put my cleaning solution inside around 100-150ml very small amount and then tossing a pcb inside the same bag. then i put the bag inside the ultrasonic cleaner. this way i can get away with very small amount of cleaning solution and save it for later in the same ziplock bag. So far it works i would say as good as a professional looking PCB but there are some caveats. I tried IPA, Acetone, Ethanol and water based PCB cleaner solution(the one i linked above) all in separate occasions to test them individually.
1- IPA(%99) and Ethanol(%90) works equally well final product is squeaky clean after 3 mins. which i could not get the same result with just a brush. its not even close, im not sure if it is the ultrasonic action or 60C heat but theres a day and night difference between brushing and ultrasonic method.
2-%100 Acetone, this one was an experience at 60C ziplock bag started to expand because acetone started to boil. this boiling action did not happen with IPA or ethanol. Final result was again squeaky clean and it did not melt anything it didnt even remove silk screen. my pcb has 0603 parts qfns and tqfp packages. didnt have plastic switches or connectors unless im out of IPA or Ethanol i would not use acetone not because its harmful for the pcb but it is scary to work with. I will probably gonna make one more try with room temp water and see the result of cleaning. Because that boiling and expansion was scary.
3-Water based PCB cleaner made a huge gummy mess it made it worse than before so i dont know i was so disappointed because its the most safe solution to work with but NO! simple as that.
4-Soapy water with purified water again it did not make any effect even after 6 mins it was the same.

So bottom line in my experience IPA or Ethanol is the way to go. i only wonder if heat is the key thing here or the combination of ultrasonic +ipa. for that my next try will be the same setup but without heat to identify which has the key role in this awesome result.
this image was taken after 5 minutes brush with IPA+acetone:

And this is the same board after only 3 minutes in ultrasonic cleaner in IPA:

@NeverDie i can speak for arduino side im not sure how it works for CircuitPython. virtual hard drive part is only true if there was a bootloader prior to update. im not sure how nordic ships their dongles but i think they dont install adafruit bootloader inside of them so you need a fresh bootloader install and it is easy but you need jlink for that. after connecting your jlink to nrf52 open the arduino from menu find jlink for adafruit nrf52 and then just simply click install bootloader and voila it works with arduino.
but then again that usb dongle wont work seamlessly with adafruit bootloader because im sure adafruit has different pin maps you just need to check their pins from variants file and match them on paper to the dongle so when you write your code you know which ones to use, unless theres a seperate variants file specifically made for this dongle.

after abit of looking around and testing i think i made it work at least examples are quite responsive without a single disconnect. i had to add some header files and extra bit of code to every sketch so the knows how to use PA/LNA.

static void pa_lna_assist(uint32_t gpio_pa_pin, uint32_t gpio_lna_pin)
{
    ret_code_t err_code;

    static const uint32_t gpio_toggle_ch = 0;
    static const uint32_t ppi_set_ch = 0;
    static const uint32_t ppi_clr_ch = 1;
    
    // Configure SoftDevice PA/LNA assist
    ble_opt_t opt;
    memset(&opt, 0, sizeof(ble_opt_t));
    // Common PA/LNA config
    opt.common_opt.pa_lna.gpiote_ch_id  = gpio_toggle_ch;        // GPIOTE channel
    opt.common_opt.pa_lna.ppi_ch_id_clr = ppi_clr_ch;            // PPI channel for pin clearing
    opt.common_opt.pa_lna.ppi_ch_id_set = ppi_set_ch;            // PPI channel for pin setting
    // PA config
    opt.common_opt.pa_lna.pa_cfg.active_high = 1;                // Set the pin to be active high
    opt.common_opt.pa_lna.pa_cfg.enable      = 1;                // Enable toggling
    opt.common_opt.pa_lna.pa_cfg.gpio_pin    = gpio_pa_pin;      // The GPIO pin to toggle
  
    // LNA config
    opt.common_opt.pa_lna.lna_cfg.active_high  = 1;              // Set the pin to be active high
    opt.common_opt.pa_lna.lna_cfg.enable       = 1;              // Enable toggling
    opt.common_opt.pa_lna.lna_cfg.gpio_pin     = gpio_lna_pin;   // The GPIO pin to toggle

    err_code = sd_ble_opt_set(BLE_COMMON_OPT_PA_LNA, &opt);
    
}

in this form i like the ble, without pa not so much. theres just big down side which is nrf52840 definitely not hobbyist friendly. next time i may design a quick nrf52832 pa board (this one has regular QFN package) to test with the same setup and compare the results.

@NeverDie i had to use stencil because i cant inspect aQFN soc from outside. as you can see every pin is at the bottom of it and they are very tiny. to make sure theres correct amount theres no other way than using stencil. to be honest i was expecting problems but it was ok

hey guys, i finally assembled my nrf52840 pa board. it was sitting there for quite some time but i couldn't find some spare time to get on with it but here are some experiences i had.
i was worried about this aQFN footprint but it all went well, looks like everything is soldered correctly and i ordered my boards with cheapest HASL instead of ENIG.

then i uploaded the adafruit feather bootloader to test the bluetooth and it all works ok. i used my iphone 6s as a central device and im not sure if my phone has LNA or PA module inside for bluetooth so it may or may not be better if i use another module like the one i did. this connection is from my module to my phone WITHOUT PA activated at tx power max(8):

and this is after i activate PA chip on board :

and this is with 3 solid walls in between at around 10 meters distance

as you can see signal strength is massively different pa bumps up the signal from -87dbm to -30dbm which is probably day and night difference.
but with this setup you manually have to enable and disable rx and tx pins in order to keep the communication. well im not really good at coding but im going to try make the whole thing automatically because nordic already has this PA assist feature buried inside its BLE core, just gotta find a way to make it work.

final board, forgot to add i opted to use pcb antenna but i could switch to external antenna as well i just have to reposition the 0 ohm resistor to use that SMA on the side and then results could get even better:

@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