I should have added, we used via fill for via-in-pad applications for surface mount components.? In this technique, a via is connected directly to the pad.? This technique makes the signal pad much shorter compared to the conventional "dog bone" structure used with pad connection to a via for through hole applications or a conventional route to a via used in surface mount applications.? ?If the via is not placed on the pad, there is no need for via fill in surface mount applications, which adds manufacturing? complexity and additional cost.? Many of our pc board were very high speed (tens to hundreds of MHz and a few GHz) with lots of layers and we made extensive use of via-in-pads. Attached photo courtesy Sierra Circuits.
-Steve K1RF
------ Original Message ------
Date 7/19/2024 7:22:34 AM
Subject Re: [QRPLabs] QMX+ Manual - BS170 - solder only 2 pins?
Often in mil applications, vias are fill with conductive or non-conductive material.? Most of the high density PCBs I worked with had vias that were filled with a conductive epoxy.? It enhanced reliability.? See link below.
-Steve K1RF
------ Original Message ------
Date 7/18/2024 8:17:50 PM
Subject Re: [QRPLabs] QMX+ Manual - BS170 - solder only 2 pins?
I grew up with MIL-STD 883B. We had to have large enough plated-through holes to guarantee that solder from one side of the board would flow smoothly through to the other side. Solder filets were visually inspected for every component on both sides of the board to ensure shiny connections. We found the hard-way that failure of the solder to flow through to the other side was usually due to the component leads being too large in comparison to the hole diameters, preventing the solder from flowing around the component leads properly and resulting in cold solder joints and/or solder blobs. I remember one project where a multilayer board with this issue was rejected by our QA people and the entire board had to be redesigned. Ouch!
Many years ago the company I worked for had a contract that required all vias be completely filled with solder. This was in the 70’s and vias were a bit bigger.
Larry
KB3CUF?
Military standards have much to say about how much of the plated holes should be full of solder (usually 75% or more although NASA likes 100% every time )?
?
In hand assembly it’s hard to control this from the other side of the board with different heating curves etc but as I said if the joint on the reverse is a good one it should be at least part filled and fine. ?
Perfectionists might like to add a bit more solder from the transistor side then suck the new excess off the bottom side then repeat ?….. ? but you can go on like that all night ?and all the time the component’s getting cooked?
