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  • Author Author: genebren
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Trying out some new assembly techniques - SMD/SMT build.

genebren

Back in October, was sharing his prize from the project14 'Electronic Toys for Fun and Learning' competition which gave me some ideas to speed up my soldering/assembly process.  As a result of that conversation, I started looking for small containers for SMD/SMT parts. What I found were these:

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It wasn't until recently that I had an opportunity to try these out.  I had just received a request from a client to replenish stock on a DMX-based motion sensor/trigger, so I had ten boards to assemble.  Having ordered PCBs and acquired any necessary parts, I set out to assemble the boards.  First, I placed most of the fine pitched components (USB jack and all of the active components.  This left me with 38 passive components that needed to be applied to the top and bottom of each board.  In the past, I would drop components, one at a time, to a side of the board and solder them in place.  This time, I decided to take each component type and drop the required quantity of them into individual containers.  Prior to filling the containers, I decided to mark the container lids with the necessary information (taken from the BOM). Here is a screen shot of the labels:

 

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Each label contains the part name(s), the component value/description and the quantity required (for each board).  The target labels were Avery 15667, 1/2" x 1 3/4" clear (return address labels).  These labels were split into two labels halves, with borders drawn to simplify the cutting that would take place, prior to placing them on the lids. Here are the labeled containers:

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Ready to give it a try!  Here is a picture of the Microscope, board holder and part containers ready for action (my soldering iron is just visible on the right hand side of the image):

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My plan is to fully populate the top side of the board with all of the passive components and then flip the board and populate the bottom side.  After all the boards are populated, I will go back and add the bulkier items (power/DMX connectors and the PIR sensor).  To start, I add solder to on pad on each of the component footprints (top most or right side pads) in preparation for placement. I then open one container at a time and place the component(s) as close to the footprints as possible using my tweezers (just to the right of the container in the above picture).  I repeat the process for all of the components on a side.  Then I use the microscope to fine tune the part placements (flip components face up where appropriate).  I then proceed to hold the components in place with the tweezers in my left hand, while I re-heat the pad (with solder) using my iron in my right hand.  I then position the board holder to center the next component.  When necessary, I rotate the board holder 90 degrees and repeat the process for any components that were up/down oriented.  Once all of the components are tacked in place, I rotate the board again and solder the other side of the component (I also touch up any of the joints for the first pad if it needs it).

 

With the top finished, I flip the board and repeat the process on the bottom.

 

While this process is a marked improvement on my earlier process, it is by no means perfect.  A couple of thoughts that I had after completing the boards are as follows:

  1. On the lid labels, add a component count for top and bottom sides, so that I know how many of the parts to pull out.  I did find a couple of times that I did not have all the parts in place when I went to align the components.
  2. Add lid labels to BOM so I did not have to do so much editing to get the label text correct.  (or build a script/program to process the information from the BOM)
  3. Come up with ruler-like device to mark out multiples of ten on the component tapes, so I don't spend so much time counting when filling the containers.
  4. For larger boards, or boards with more components, maybe it would make sense to have separate containers for top and bottom sides of the boards.
  5. Do a better job of numbering components, maybe even adding a 'T' for top and 'B' for bottom to the entries on the BOM (and then the labels), as I spent a lot of time locating the components on the PCBs.
  6. I was a little less than happy with the container bottoms, as they had rough spots (sprue marks) that and tight corners that made picking up parts difficult at times (not sure what to do about this yet).

 

Also, I was a little disappoint in the lid mechanisms on these containers.  First several of the lids where broken (missing hinge pins) and some of the lids did no pop open freely (some needed a little help opening).  But all in all, things went fairly smoothly.  Here is a picture of the fully assembled and tested boards getting ready for shipping:

 

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I tried not to build too many boards, but I do find a need from time-to-time to build batches of board (10 - 25) at a time.  I will continue to hone this process and I will share any ideas as I come across them.

 

Gene

  • in reply to Fred27

    David,

     

    They are of questionable quality.  I will continue to look and check out the ones that you mention.

     

    One of my good friends has done a lot of work with the toaster oven (and halogen lights - very hot) to solder boards.  I have seriously thought about looking into this as a way to approach higher assembly volumes, but I have not taken the plunge just yet.  I have used a hot air system some years ago (at work) to solder on high pin count and tight pitch parts, but again for home usage I have not used this approach.  About a year ago, one of my clients wanted to build up lots of 100 boards.  At the time, I referred him to an assembly house, which turned into a complete disaster, needless to say he is not longer a client as I guess he held that experience against me.

     

    Thanks

    Gene

  • in reply to DAB

    DAB,

     

    David is right, it seems a lot more difficult, but with time and good tools it is a lot easier.  I do understand that we all do have special conditions that we must overcome, but again with time we can manage.

     

    Gene

  • in reply to jw0752

    Hi John,

     

    Thanks for the comments.  I too am a big fan of hobby stores and frequently looking for craft related items that I can use for storage and tools/supplies.  Here are some of my other favorite storage solutions that I have found in hobby stores:

     

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    To the left are stackable (screw tops and screw together) containers intended for beads, that I have used to store either parts relating to a specific project (in this case Light Rings for Microscopes, like the one pictured in this blog) or for collection of parts (resistors, capacitors, diodes, etc).  To the right are embroidery thread containers that I use frequently for hardware and consumables that I use frequently.  I have 15+ of the bead containers and 10+ of the embroidery thread contains that contain a lot of my stock.  All these containers and I still need more to keep up with the constant steam of stuff that I try to stuff into my office.

     

    Thanks again,

    Gene

  • in reply to genebren

    The lids fit very tight and the box folds in half and clips tight shut - I can't imagine that dropping from height would cause spillage, even if the box itself broke open, the compartment lids would stay shut.  But yes, at that price several hundred parts would cost a fortune!  They would only fit SMD parts because the compartments are tiny.

  • in reply to three-phase

    Thanks Donald.  I am always looking for storage solutions, so I knew I will continue to look for others (as I am sure most of us are and/or will).