Operation Want It Yesterday

Psycho Hot!

Figure 1: Line of plated through holes with no connections.

Here is something you haven't heard before, "This job, is hot, burning hot, blazing hot, psycho-hot!"

That's what this job is, hot, hot, hot. So let's get to work.

The problem is the board was made like the picture you see in Figure 1. It may not clear in the photo, as connections can be buried, but the featured plated through holes (A through V, Row 1 through PS) are supposed to be connected to ground in order to properly perform their function. They're not connected to each other or to ground.

Figure 2: Milled trough with connecting copper circuit laid in placed.

It would seem easy enough to find a ground point and connect the pins once the board is populated, or to just buss a wire along the row of pads. But! The customer's customer nixed both of those ideas. What's required is a connection on the bare board, one that is rock solid and does not interfere with the barrel of the plated through holes. And the whole row has to be connected to ground on layer 3.

One other thing, the pads, from their edge to the inside of the plated through hole (PTH) are only about .010". That's pretty small and would make it difficult to solder a wire or circuit to the pad without getting solder into the hole. So here's what we'll do, we'll mill a trough down the row of pads. Then, very carefully, under high magnification, we'll excavate under the each of the PTH pads in order to tuck the connecting circuit to the copper of the PTH without getting solder into the hole. See Figure 2.

Figure 3: Ground plane exposed and copper circuit in place for connection.

That's a nifty piece of work and requires a patient, steady hand. But it must be done fast, for goodness sakes! The customer's on the phone asking status. Additionally, at the end of this row of plated through holes we will use a precision milling system to mill down to layer three in order to expose the ground plane for connection.  The connecting buss will be soldered to the ground plane and run out to the row of plated through holes. See Figure 3.

So a well tinned copper circuit is laid in the trough, and carefully soldered to the underside of the barrel and pad of each plated through hole.

Figure 4: Circuit run out to ground and masked.

Once that is complete the circuit is connected to ground. That portion of the rework is visually inspected and metered. Then the circuit is secured in place with high strength thermosetting epoxy and masked to blend in with the board.


Figures 4 shows an in-process view of the ground connection and Figure 5 is of the line of plated through holes bussed together.

Figure 5: Complete row bussed.

So there it is, good stuff, done right and done quick. One more fire quenched!

Several members of the Circuit Technology Center team contributed to this feature story.