Monday, November 9, 2009

Hemostats - The Third Hand You Always Need When Assembling Electronics

I've used hemostats for years for a variety of tasks. One of the most common uses has been to hold components in place for soldering when assembling an electronic kit.

When I found these compact, well made and inexpensive hemostats, I decided to add them to our Wildhorse Innovations store and write this blog about their use.

For those of you not familiar with hemostats, they were first invented for use as a surgical tool.  They are the pliers like surgical tool that doctors use to, among other things, clamp off blood vessels during surgery.  They are made in many sizes with a variety of jaw shapes.

The handles of the hemostat have a set of interlocking fingers designed so that the hemostat automatically locks in a ratchet like manner as they are closed.  The fingers have several ratchet grooves that allow the hemostat to apply varying amounts of grip as they are closed.  To release the hemostat, apply pressure to the handles (as if you were closing them) and move the handles slightly apart so as to release the ratcheting fingers.

When assembling electronic kits I find the hemostat most useful for holding components with stiff legs (such as a voltage regulator in a TO-220 package).  They are especially useful for holding pin headers that not only have stiff legs but also very short legs.  Depending upon the circumstances I may use them to hold DIP ICs in place for soldering.  I almost never use them to hold components with long, flexible legs such as resistors.  It is much easier and quicker to just spread the legs after inserting the component through the holes.

Hemostats are not a "must have" for the electronic enthusiast. Some people advocate using the "heat and plunge" method of inserting items such as headers. Using this method, you cover one of the holes with solder, then while holding your soldering iron in place to maintain the solder in a molten state, you quickly insert the header into place. I've used that method at times, but after many burned finger tips, I decided that hemostats were the way to go, no matter what the cost. The low price of these hemostats take cost out of the picture.

Speaking of pictures, I have inserted some below to show the use of hemostats. They are of my usual non-professional quality, but they get the point across.

The first two pictures show hemostats being used to hold a TO-220 voltage regulator in place for soldering. Pin headers and ICs are shown later in this blog, but the procedure is about the same for all devices.

The top picture shows a side view of the voltage regulator held in place by the hemostats.  The voltage regulator is a little slanted but we will correct that later. The  bottom picture shows the view from the bottom of the board.

From here on, the procedure is quite simple.  Solder ONE leg of the voltage regulator.  While the solder is still molten you can use the hemostats to adjust the placement of the component.  As an alternative, you can remove the hemostats and reheat the joint while adjusting the placement with your free hand.  Now solder the 2nd and 3rd pins.  After you have finished with the last two pins, go back and reflow the original pin.  Since you were adjusting the position of the component while this joint was molten, there is always the chance of getting a cold solder joint.  Reflowing after the component is solidly in place eliminates this possibility.

The next two pictures show the same procedure, this time used on a pin header.  One big advantage the hemostats have in this situation is that the bottom if the pin header is designed to seat flush against the surface of the board.  Letting the hemostat hang off the side of the board pulls the pin header toward the surface of the board.  With a little practice you can hve the pin header seated properly the first tme, everytime.

But don't forget to reflow the first joint soldered.  Even with the pin header securely seated, there is always the chance of a slight bit of movement causing a cold solder joint.

The next two pictures show hemostats used to secure an IC for soldering.   The procedure is slightly different for this type of component.  With the hemostat holding the IC in place, solder two diagonal corner pins.  The remove the hemostat and while pressing the IC towards the surface of the board with one hand, reheat the two solder joints and allow the IC to seat firmly against the surface of the board.  Solder the balance of the pins and reflow the first two.


OK, that's the end of today's lecture.  I hope you've paid attention.  You never know when there might be a pop quiz.

One last thing.  Hemostats make great heat sinks when you need to isolate a component from the heat of soldering.  Today's components are pretty tough when it comes to soldering, but there once were components that were very sensitive to heat and could easily be ruined during the process of soldering.

As always, you comments and opinions are welcome.

1 comment:

  1. Soldering is general to many manufacturing processes. There are many different soldering techniques required. One rule that applies to all of them is "don't burn your fingers." To avoid this accident, hemostats are frequently used.