A stereo microscope

Wow. I didn’t really think I needed a “real” microscope. So far for working on those tiny SMD components I’ve got by with a jeweller’s loupe and a magnifying headband from my father-in-law who is a retired dentist. For inspection afterwards, I used a £20 eBay USB microscope. This all seemed adequate.

However, for the latest version of my NFC login project I had to solder a TRF7970A NFC transceiver. These only come in QFN package. The 0.4mm pitch pins aren’t too much of an issue. I can handle these OK on the LQFP package that the MSP430 comes in. It’s the fact that there aren’t actually any pins sticking out – just a visible metal pad on the lower edge of the chip. I had to rework one a few times as I hadn’t got it quite right and I suspect I was starting to do some damage to the chip and/or the PCB.

I did a bit of research – mostly on eevblog. The really good ones are way to expensive for the amount of use it. The good value AmScope models that most people recommend are too expensive to ship outside the US. Brunel microscopes in the UK seem good, but still quite pricey. Then I stumbled across the usual eBay “bargain” direct from China. I’ve been happy with the price/quality compromise on the laser and CNC mill I got this way. Time to dig a bit deeper and see of this is likely to be a good idea.

Microscope1I found a very helpful review on eereview that served to be the same model. To be honest, it seems the same as some of the AmScopes too. It actually looks the same as the BMDZ series from Brunel too. I decided to risk trading off quality for specifications and went for it.

Here’s the image straight from the eBay listing. I assume the seller won’t mind as I’d be happy to recommend lapsun_gift. The microscope (plus some x0.5 and x2 barlow lenses) arrived in about a week. It was marked a $95 but form some reason UK customs decided to charge me VAT on £125. The cost was about £300 so I was OK with that. The same microscope without camera, ring light or barlow lenses was £450+VAT in the UK so I was happy with the price too.

wpid-wp-1448207092901.jpgI’m very happy with it. Inspecting a reworking LQFP used to be a pain. My USB microscope would allow me to see stuff but the lighting meant I couldn’t really be sure what was a short of solder and what was a reflection. The actual soldering had to be done with no magnification and then re-inspected. Now I can actually see properly. The microscope itself is 7x to 45x zoom. With the 0.5x lens I get less magnification and a 165mm focal length and can actually solder under it – whether an iron or hot air. Zooming in (and perhaps removing the barlow lens) means I can actually see the individual balls in the solder paste.

The 2x lens (i.e. up to 90x magnification) is a bit much for anything other than really detail inspection of a PCB. It should be great for counting a spider’s eye with my boys though – if it’s not too scary!

WIN_20151122_16_23_58_ProThe camera is probably the weakest point of it all. When switching the camera in, you lose one of the stereo eyepieces. Not really a problem. However, I find the the image the camera sees is about 10% of what you see through the eyepieces. Focusing is tricky and I can’t see to get it to focus at the same place as the remaining eyepiece. In the image shown each pin is about 0.2mm with 0.2mm gap to the next one. Through the eyepiece you can see the whole 48 pin chip and some passives around it. It’s also far clearer. That photo really doesn’t do the microscope justice. Never mind – the camera was just a “why not” addition. I might try an adapter for my SLR camera at some point but no hurry.

Many people recommended a boom stand. This didn’t come as an option with the eBay model, but if I ever need one I can always add one later. The supplied one is certainly adequate for me so far. If I need to look at an angle I just tilt the board and refocuscam.


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