Am 26.01.22 um 04:39 schrieb
jla...@highlandsniptechnology.com:
> On Tue, 25 Jan 2022 23:40:32 +0100, Gerhard Hoffmann <
dk...@arcor.de>
> wrote:
>
>> Am 25.01.22 um 23:08 schrieb John Larkin:
>>>
https://www.dropbox.com/s/idwz568o8hfpgzb/TDR_Solder_Mask.jpg?raw=1
>>>
>>> The two un-masked patches are not visible on 30 ps TDR. Board
>>> variations are a lot bigger.
>>
>> I got similar results on a JLCPCB 4 layer board.
>> I calculated that 50 Ohms are 11.55 mil, drew it 12 mil in
>> Altium. Seems to fit.
>>
>> <
>>
https://www.flickr.com/photos/137684711@N07/51843174578/in/dateposted-public/lightbox/
>> >
>>
>> The SMA launcher decal was not so good, but I was interested in the 50
>> Ohm line only for verifying eps-r and thickness etc.
>> The launchers were for a 2 layer process. The streamlined boards
>> for the LMX2594 are on the plane from HK. They also have cutouts
>> on Layer 2 and shorter SMA center pads. The unpopulated SMA is
>> better than the populated one. The thickness of the center pin
>> and the solder seem to matter.
>>
>> cheers, Gerhard
>
> The quickie Chinese board houses default to super thin layer 1/2
> dielectrics for some reason. If you use layer 2 as ground, that makes
> your SMA pads capacitive anomalies. Even the cutout doesn't seem to be
> enough; fringing maybe.
That is needed to get some signal out from under a BGA.
They also have a process for thicker lines. I think I will
test it with a UHF LDMOS power amplifier.
<
https://www.flickr.com/photos/137684711@N07/51844498620/in/dateposted-public/
>
one of the next tries. Red is top = 1, blue = 2,
yellow = 3 (not in this area) 4 = bottom = green.
Looks like the center pin on my board. I also have recovered
some SMAs from junked wafertesters; they have REALLY small
center pins and a ground tunnel / bridge with 2 hex nuts.
They might fit the 12 mil line directly. Probably a solder
problem even with the finest METCAL tip.
Probably Rosenberger.
The plane with the new boards has landed in .de in the night. :-)
Cheers, Gerhard