The above photo shows several copper box enclosures that were hand made to support a radio transceiver project called JABOM. This transceiver is a 5 watt QRP SSB Transceiver that can be used on either 17 or 20M. Great care was taken to isolate the various stages and this was accomplished by using individual circuit modules that were enclosed in copper boxes.

The boxes are built from double sided PC Board purchased in bulk from eBay. A three pound box (lots of material) was purchased for $10 including shipping and featured a stack of various sizes most in the 4 inch by 8 inch range. This is a perfect size for building the small boxes. Six tools were used to fabricate the boxes. These include a hacksaw with 32 tooth (fine cut) blades, a plastic miter box to enable straight cuts, an adjustable square, a mechanical pencil, a hand file and a dust mask. DO NOT BREATHE THE DUST generated from cutting the PC Board. A shop vacuum would be the 7th tool.

Two approaches are used for the circuit boards housed within the copper boxes each of which will be described in detail. The first involves the use of single sided vector board where the copper top side is used as a ground plane and all connected wiring is done on the reverse insulated side. Because of the exposed wiring on the underside this board cannot be placed flat on a chassis as it would short the wiring. This method includes a means to elevate the boards as you will note with the aluminum threaded pillars shown in the right hand photo.

 

The second method entails the use of copper islands ala Manhattan style construction and in this case the PC board is simply mounted to the chassis using mounting holes in the four corners of the board and the copper box is built around the board.

 

There are advantages and disadvantages to both methods and both were employed in the project. The more complex circuits where there are a large number of interconnects I used the single sided copper vector board. For the circuits where fewer components are used then this lends itself to the island construction. In the first photo above, three used the single sided copper vector board and three used the island construction. One of the modules, the audio amp stage did not require a shielded box and so it used the vector board mounted in a vertical plane.

Method #1 Copper Box Built Around Single Sided Vector Board

Start first by assessing how large of a piece of copper vector board will be required to contain the circuit module you are building. The process I use is to take a piece of vector board that has no copper plating on the board and I lay out the components to follow the schematic with a careful eye to minimizing any cross overs on the underside of the board. The reason for using the non-copper board is that you will be handling this board quite a bit and the acid in your hands will cause finger marks on the bright copper and after a bit will tarnish the copper surface. At first this may seem cumbersome but a few times through the process you will learn how to minimize the real estate used and the number of cross overs.

When I reach the point that seems to present a reasonable sized board, I take a digital photo so I have a record how I did it. Using this mockup board I also conveniently locate four places where I will drill a 1/8 hole in each location. These holes are located a reasonable distance from the side edges. Typically they are from 1/4 to 3/8 of an inch inboard from both sides. These holes will be used to locate 4 aluminum pillars that enable the board to be elevated from any surface. I purchased a large stock of these pillars which are tapped through to fit a 4-40 screw and are 1/4 to 1/2 inch high. When you actually go to insert parts on the copper board the spacing enables one to place the through hole components so that the excess fits underneath the board. For components that go to ground they are simply soldered to the top ground plane. For those that connect to other components the copper side of the pass through hole is enlarged slightly to remove any copper around the hole so there is no short to ground. A few twists with a larger drill bit is all that it takes to remove a bit of the copper around the hole.

It is important to build the circuit first before installing the copper box around the single sided copper vector board. This also includes installing any internal shielding on the board. Shown below is an example of what was just described. Note the shield between the IF stage and the Product Detector (SBL-1). Note also the four screws that are attached to aluminum pillars. In this case I should have actually had a little more clearance from either end. The side clearance was OK. This will become important when the box is soldered around this board to enable getting the soldering iron into the corners.

 

The next step is to figure out how high to make the copper box. Using 1/4 inch high aluminum pillars and accounting for the thickness of the board and then looking at the vertical height of various components typically you will find that the height is 1 inch total and just in case there may be heat sinks involved then it is best to consider something on the order of 1 & 1/4 inch height on all four sides.

Now this is where some careful measurement is required. For the width ends I make the sides exactly the same size as the board. For the length sides I make the total length longer than the board plus the two end plates. The reason for this is so I can solder the inside of the box as well as the outside of the box.

On the left panel you can see where the end plates are net with the circuit board. Also note that the initial set of holes I drilled in the board for the pillars were too close to the edge and I had to drill four new holes. Even I mess up more than occasionally. So profit from my mistakes. On the right panel you can see how the side piece extends beyond the assembly so I can solder the inside of the box as well as the outside of the box. This is the real advantage of the double side PC Board.

The initial copper box assembly process involves the following steps. Prior to any assembly work being done, it is important to drill various holes in the side pieces before any assembly. Holes to accommodate RCA type connectors, power feed through's and other access holes must be drilled first. Spend a great deal of time in assessing where the holes will penetrate the box, with an eye to minimizing lead lengths and above all that the items such as the RCA connectors will have clearance with the board mounted components. You don't want the center pin of an RCA connector touching the heat sink of a power transistor!

Now on to the assembly process and the first step is to position the circuit board with the pillars installed in such a manner that enables convenient soldering. When in this position I use the 3M making tape to hold the circuit board in place on the work bench. Yes I tape the board to the bench as this firmly holds the board and minimizes any damage to the board. ! Next I place a dab of solder on each corner of the circuit board. I have several small blocks of wood that I use to act as a back stop for the end plates. This also enables the end plates to be in a vertical plane with respect to the circuit board. Once alignment is done heat up the corner where the solder is so that the corners are tack soldered. Stop! Check the alignment so that the ends plates are aligned with the circuit board and that the end plates are in a vertical position. Observe the left hand photo above and you will see how this looks from the bottom side. There is a snug fit from the end plate to the circuit board and the plates are aligned with the board. Once you are convinced all is well add a couple of more beads along the seam of the two boards. Stop again to assure nothing has moved. Now you can connect the beads to form a continuous solder seam.

For those who might want a little practice before trying this procedure on finished circuit boards, take a couple of scrap pieces and run a couple of test runs to gain experience at this process. That is exactly what I did!

Method #2 Enclosures Built Around Island Construction

Both methods are very similar insofar as the height of the sides and the method of making two of the pieces longer so that soldering can be done both on the inside and outside of the box. The same process relative to drilling hole penetrations and part clearance are observed with this method. Start again by having the circuit built, completed and tested before you build the box around the board. In Method #1 you have access to the underside of the board so it is a little more forgiving relative to making changes. In Method #2 once the sides are around the board it is more difficult to access parts as the sides are in the way. That said in Method #2 the soldering process is a bit easier since the board can be screwed into a block of wood and the block of wood "C" clamped to the workbench . Again the wood blocks are brought into play to hold the vertical pieces against the circuit board and the same tack solder and alignment is observed. Solder the end plates as in Method #1 and then the sides. See below.

The Finishing Touches

Both methods provide a box that is strong, rigid and serves the purpose of providing isolation. This begs the question of what to do now with these neat boxes that you just built. We now have a choice of mounting options. Where you have a lot of real estate for a base plate then horizontal mounting of the boxes is easily accomplished. With Method#1 determine the location of the box first and the location of the 4 pillars relative to the box placement and drill four matching holes. The beauty of the single sided copper vector board is that the holes are on 1/10 inch centers. So assuming you drilled the mounting holes through these pilot holes, it is a simple matter to precisely locate the 4 holes to be drilled. Measure twice and drill once! Once that is done then simply mount the box to the base plate. In Method #2, locate the box where it should be on the base plate and drag out the 3M tape. Tape the box down so it does not move and then mark the holes with a pencil through the holes in the circuit board. Mark twice and drill once. That is it!

But in both methods a lot of real estate on the base plate is used to accommodate all of the boxes. So the other option is vertical mounting of the boxes and this will require the building of some more copper pieces. essentially the vertical mounting entails building "L" type brackets where the boxes are mounted to the vertical part of the "L". In short, base plates are cut to size that match the bottom side of the box enclosures and mounting holes are drilled to match the patterns of either method. Fasten the bottom plates to the box assembly. See below:

 

The next step in the process is to cut a strip of PC Board 1/2 inch wide and cut to length of the box. Mounting holes are cut in this strip with careful attention to not locating the mounting holes where it would interfere with the screws that attach the base plate to the box. Now locate the copper box in the appropriate location on the base plate so that the box is now sitting on one of the sides and is in a vertical plane. Assure yourself of clearance to plug in RCA connectors and routing of wiring. Once you have done this several times. Mark the location of several of the corners so you can return to this exact spot. Take your 1/2 inch wide strip and using the mounting holes temporarily mount the strip on a piece of wood using wood screws. On either end where you will solder this to the bottom of the copper box place a dab of solder. Next bring up the copper box bottom plate so it abuts and aligns with the strip to form a 90 degree angle and that the ends of the bottom plat attached to the copper box align with the strip. Insure the box is "flat" to the wood surface. Tack solder and check the alignment. If that is ok add a few more solder spots along the length of the seam. Check the alignment. If all is well connect the solder dabs to form a continuous bead. When cool remove the assembly and return to the marked location on the project base plate, mark the hole location on the base plate. Mark twice, drill once. In the photo shown below this is the BFO/CIO assembly and a top cover was fabricated using thin gauge tin plate and it was then soldered to the box assembly to make a completely sealed box.

 

Below is a photo of the copper boxes as installed in the JABOM QRP SSB Transceiver.

73's

de N6QW