Get some high-temp rubber solid tubing of the diameter of the hole. Cut them to length and insert to the desired depth. Add solder and voila! Serve with cookies and milk.



-----Original Message-----

From: TechNet [mailto:[log in to unmask]] On Behalf Of Bob Wettermann

Sent: Monday, July 09, 2018 9:24 AM

To: [log in to unmask]

Subject: [TN] Getting a hole partially filled on purpose-Ideas?



All:



We have an assignment where we need to, amongst a variety of induced  board

and assembly defects, come up with partially filled PTHs.



The objective is to partially fill a PTH on a multilayered, fairly

thermally massive board and make sure it is filled to approximately 25%,

50% and 75% of the height of the barrel. The PTHs have a 2mm hole diameter

and are 1.57mm in thickness.



We have tried to get this done by blocking a certain portion/depth of the

holes with liquid solder mask and then getting the solder to flow down into

the PTH. Subsequent to this we remove the mask. This has not yielded the

results as the mask does not really get to the right level in the hole. We

tried selectively adding solder via flux-cored wire and by the time there

is wetting all around the component lead,  the hole fills up to too high a

level. Using braid and excavating equipment to remove a small amount from

the completely-filled hole has also proven to be a challenge as it is

difficult to uniformly pull solder from the barrel all across its diameter.



One of our thoughts is to have specialty made solder preform "donuts" and

slide them into the hole.....any other thoughts from the crowd?



Thanks!

-- 

Bob Wettermann

BEST Inc