Advertisement

Blog

How to Bring New Life to Old Hybrid Circuits

A while ago, fellow Planet Analog blogger Dennis Feucht talked about integration onto ceramic substrates in his post Between Discrete & Integrated Circuits.

The comments went into a brief discussion on hybrid circuits (Figure 1).

Figure 1

Figure 1

I would like to dive into that old world that is still in use today. Companies such as Apta, Dynamic Hybrids, and MicroHybrids are still designing and assembling hybrid circuits in large volume for military, space, and other applications. One of my current jobs is to recreate old hybrids, but on a small volume scale and at a low cost. A typical hybrid, once the lid is removed, looks something like that in Figure 2.

Figure 2

Figure 2

What one sees are some resistors (black segments), traces (in gold), some diodes and/or integrated circuits, and even surface mount capacitors, all on a ceramic substrate (white portion). The resistors are built and trimmed to specification. Other discrete parts are bonded onto gold pads. The semiconductor devices are typically bond wired to a gold trace. Around the edge of the ceramic substrate are posts. The posts serve as bonding pads that allow the connection of the circuit to be made to the pins of the hybrid (Figure 3).

Figure 3

Figure 3

In order to get a hybrid made, one would have to purchase the semiconductor parts unpackaged, and most semiconductor companies would prefer to sell packaged parts since die handling is difficult in general. Also, one would not be able to buy a small quantity of die, but would have to purchase a half or whole wafer's worth, which could be thousands of parts. This is not the best low-cost method.

Since I have to recreate these hybrids that were last made 20 to 30 years ago, the challenge is two-fold. The first is finding replacement parts for the old ones. The second is how to package for a low-quantity production.

My solution ended up being quite simple with today’s component technology. Granted, for the first challenge, finding an op amp that meets the exact criteria as the old can be very difficult, but not entirely impossible, with additional circuit modification, if necessary. Same with obtaining odd-ball resistor value, not in the 1% value chart, but this can be accomplished by careful selection of two resistors in series or parallel.

The second challenge, packaging, ended up being the easy part — we made a circuit board instead of a ceramic circuit substrate. There were further complications and tricks regarding how to package everything onto the PCB. The circuit board would then be inserted into the hybrid package, as shown in Figure 4.

Figure 4

Figure 4

Now a little bit of adjustment of dimensions would get back to that final packaged part.

So, there is an old problem part moved into the modern era with a low-cost solution. What have been your unique solutions to old problems?

20 comments on “How to Bring New Life to Old Hybrid Circuits

  1. D Feucht
    January 25, 2014

    Derek,

    Your work illustrates the simplification of electronics over the years. I noticed that your circuitry did not require the thermal conductivity or high resistance of a ceramic substrate, and that you could use a FR4 (or G10) board instead. With surface-mount parts and the small clearance distance of circuit-board traces and pads nowadays, there is essentially no disadvantage in using etched boards where hybrids were once used.

    Laser trimming of resistors is nice but not an essential feature of hybrids because resistors have also improved and can be specified for tight tolerances without a high cost. (0.1 % resistors typically cost about $0.25 in low quantity.)

  2. RedDerek
    January 25, 2014

    Considering that the hybrids I work with are 20 to 30 year old designs, the replacements I am working on are not that critical. Back then the goal of hybrids was to compact circuitry in order to fit the space allowed. My task is to make the new products look as much as originals whild still maintaining form, fit and function. FR4 is sufficient to meet the requirements. There is shielding due to the packaging method as well. In the last seven years I have developed replacements for a dozen parts so far without any failures in the field.

    The initial issue was, can all the new parts fit in the package. There was a stack-up calculation to check that everything can fit within the height of the current package. Other mechanical requirements were reviewed as well.

    I agree that the use of 1% and tighter resistors are more than adequete to meet the requirements of 20+ years ago.

  3. Netcrawl
    January 25, 2014

    Design and materials are parts of performance challenges, that's why there's a great need for new approach on system design to meet future requirements, traditional solutions are running out of steam- we faceproblems associated with power requirements, signal loss and etc. We're still in chip-scale era but there's something new coming to industry-packaging in 3D, with 3D I think it got the potential to change everything. 

  4. amrutah
    January 25, 2014

    Derek,

       I had never heard about the Hybrid circuits and thanks for the blog post.  It would be helpful if you could share few tutorials on this topic.

     

  5. Victor Lorenzo
    January 26, 2014

    @Derek, I find very interesting your job. I've been lucky enough to have in my hands a lot of different electronic components, but only a couple of them were hybrid modules. It was about twenty years ago, so it was at that time “state of the art” integration technology and we got excited to crack one open and look inside.

    It will be very nice reading about the process you follow for reverse engineering and redesign.

    Thanks for the post.

  6. Vishal Prajapati
    January 29, 2014

    I also haven't heard of hybrid electronics parts. But after a bit of googling I found that I had used one part which was DC/DC converter for the IGBT gate driver ckt. That was around 10 years old circuit and I didn't even knew the manufacturer. I just had a PIN out and it was working fine. Later we replaced it with buck converter. Which looked something like this Orange part.

     

    Hybrid Circuit

     

     

     

     

    But nice and interesting way of reverse engineering of obsolete parts. Reverse Engineering is a big headache for young engineers like us frankly.

  7. SunitaT
    January 31, 2014

    @Derek, thanks a lot for the post. Really informative. I have never used hybrid circuits. Are you planning to write more blogs on this particular topic ?

  8. SunitaT
    January 31, 2014

    Reverse Engineering is a big headache for young engineers like us frankly.

    @Vishal, I agree with you. I think colleges should also teach more about reverse engineering aspects to the students. This helps them to explore more about the old circuits and products.

  9. David Maciel Silva
    January 31, 2014

    It's really a job in engineering. I often joke saying that engineer and who can improve something, change so that it is cheaper, but with the same features, electronically saying is admirable.

    Making connection of integrated circuits is easy, it's hard to hit a scaling, where there is the magic.

  10. RedDerek
    January 31, 2014

    @Victor – Unfortunately my hybrid process is somewhat proprietary and I dare not go into much details. The company I consult for has a unique special niche in the market it serves. Suffice it to say that it does take some time to ensure newer parts will work in place of the old parts. However, a 10 MHz opamp now does not necessarily replace the one from 25+ years ago. And layout can be critical.

     

  11. RedDerek
    January 31, 2014

    One can learn much looking at how someone else did something. I continually do reverse engineering for one company. They have more projects coming that will be even harder to do – one may involve point-to-point Ohm checks since there is no documentation expected.

  12. RedDerek
    January 31, 2014

    @Vishal – the orange part is considered a hybrid. One can argue that integrating two or more parts into a package is a form of hybridization. Semiconductor company do this quite often, even in the discrete products – MOSFET + Schottky, and even the DRMOS products. Hmm, maybe an article on these may be of interest. I am sure I can find some old pictures from my semiconductor days.

  13. Vishal Prajapati
    January 31, 2014

    @Sunita, the colleges are not even teaching the forward engineering. Not even how to design a proper circuit using practical cases. By teaching reverse engineering it would be even confusing for students to learn weather they should design a circuit from scratch or find a ready made circuit and get it reversed to make a copy for themselves.

  14. Vishal Prajapati
    January 31, 2014

    @RedDerek, I didn't knew about Power devices comes in the hybrid packages. Because now a days I generally see and use the MOSFET in a standard TO220 or Dpack package having integrated Schottky diode. I though only big circuits like DC/DC converters and signal isolators would be comming in the hybrid packages.

     

    Is there any standard for hybrid packages also? or they are just made SIPs and DIPs?

  15. Vishal Prajapati
    January 31, 2014

    @RedDerek, Sir, reverse engineering is an art which can only be mastered by continuous and long practice. To reverse engineer a smallest circuit need deep knowledge of old and new components and their characteristics and should have extensive hands on experience of designing of different circuits.

     

    Even to observe someone doing reverse engineering for Analog is scarce now a days atleast for me. I now understand how difficult it would have been to provide design/repairing support to Militaries and Aviation Industries for so long times like 20 year or sometimes 25 years.

  16. RedDerek
    January 31, 2014

    @Vishal

    I now understand how difficult it would have been to provide design/repairing support to Militaries and Aviation Industries for so long times


    This type of work has been my focus the last seven years. I enjoy the challenge. Once in a while it become VERY challenging because certain key drawings are not available and thus, the resort to guessing. Sometimes I hit it right the first time. Sometimes it takes a few cycles or even a trip to the customer's facility to use their test equipment and make comparison checks.

    But, it is FUN! That is what keeps me going. I enjoy the challenge. Afterall, if it was not for problems, engineers would be out of work; so accept the problems to be solved.

  17. RedDerek
    January 31, 2014

    @Vishal

    Is there any standard for hybrid packages also? or they are just made SIPs and DIPs?

    No formal standard that I have seen. Use of a common package is used, but, as  you noted, there are SIP and DIP version – usually on standard pin separation grid such as .050 or .100 inch.

    Semiconductor companies will hybridize two or more die into the same package. Tear apart a most dual MOSFET SO-8 package, there are two discrete MOSFETs within.

  18. yalanand
    January 31, 2014

    reverse engineering is an art which can only be mastered by continuous and long practice. 

    @Vishal, I totally agree with you. Reverse engineering is very difficult and I think it requires lot of experience and infrastructure. But I really wonder how Chinese have mastered this art of reverse engineering.

  19. studleylee
    January 31, 2014

    @Vishal P: I totally agree. I was lucky to have spent many years in repair prior to finishing my degree and moving to system design.

    In repair often it was cost prohibitive for the repair to stock all the schematics for everything, so reversing was needed for both Analog(music amplifiers etc) and digital( TV, media players, etc ).

    This was a perfect way to see how manufacturing designers think and went about impleneting functions. You could see styles in Sony vs Samsung vs many others.

    Repair also gives you many mechanical design insights.

    You get to see the weak points that cuased the repairs to be needed. Often I had to make a better version of the circuits as some customers are very attached to personal electronic items that they have owned over time.

    Repair has change much in the past decade toward disposable electronics so you need to wear many hats today to make a living and be needed for job security.

    To be securely relevent today, I'd suggest students to be able to develop multiple skills: repair, design(CAD SCH,LAYOUT), handworking mechical and mech CAD, and hobbies that promote these strengths. This can make you layoff proof and able to start a business if needed. -Lee Studley

  20. studleylee
    January 31, 2014

    I love reversing STKxxx amplifier and TV vertical/horizontal drive amp modules. They are good examples of how to build HV opamps via discretes.

    It's hard to get a good High voltage opamp on the order of +/- 60 volts or more without paying alot for the device. Though LTC has some good ones lately.

    Using Spice( LTSpice ) you can build them up and calc and play with values to see the biasing and respones.

    A true geek's puzzle 🙂 Great article!!!  -Lee Studley

Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.