The video above covers this in detail, and we follow a similar process apart from:

• We use a nail file to smooth the cut edges of the PCB, a Dremel is not necessary.
• We use one of the offcuts of the PCB as a paste spreader, it works fine. And hence we don’t bother cutting the stencil and making a “posh spreader” like shown in Phil’s video.
• For countersinking of the microphone hole we use a cordless drill with a countersink bit in it. This works well. No Dremel needed.
• We still use superglue rather than hotmelt to fix the PCB offcuts in place to hold the PCB. It’s quicker, just work fast!
• When attaching the PCB offcuts we like to ensure that the full area of the stencil is supported, using extra offcuts around the side. This prevents the edges of the stencil being pressed down and raising the middle when applying solder paste.

If when lifting the stencil you see the solder paste has crept between the pads, and is making contact between them, then the best option is to wipe off the solder paste and start again. Make sure you clear the mic hole of any residual paste before re applying. The key places to check are the Microphone and the Integrated Circuit (IC) pads. Holding down the stencil firmly when applying paste will help prevent “creep”.

Likewise if during assembly, the paste is smeared, then it is usually best to remove the components placed and wipe off and start again.

Having said this. as the solder paste melts, capillary action draws it strongly towards the pads, and we have seen, for instance a mSD card holder where all the pads were bridged in one solid lump of paste, work out fine after the paste was heated. So (with everything except the Mic and Pico) you can sometimes let smears go, so long as the component is placed accurately on the pads.

We are a firm believer in doing the hardest components first, the most accurately placed, largest or ones in tricky locations. Then if an error occurs and you have to wipe of and start again, you have lost the minimum of effort.

We have developed an order that works for each device and on each device component layout we say “start at the top and work down”. In general this is:

• Raspberry Pi Pico
• mSD holder
• Switch
• 3.5mm Jack
• Microphone
• IC Op. Amp
• Capacitors
• Resistors
• Ferrite Bead
• LEDs

You will receive packets of components that say “electrostatic sensitive devices, do not open or handle except at a static-free workstation“.

While is is true that large amounts of static electricity could in theory damage the components, in practice they are quite robust and unlikely to be damaged by normal handling.

So we take no special measures at all, and ever with Integrated circuits, LED and Capacitors, and have never had a problem.

However you might as well take simple precautions such as:

• Leaving the components in their strips, in the antistatic bags, until you are ready to use them.
• Only opening the component strips over a blue Antistatic mat, and dropping then directly onto the mat.
• Only using anti static tweezers to pick up the components

On the nano and mini Pipistrelle, and newest Griff and mini Griff the answer is no. They all use standard ceramic capacitors with no polarity.

The PippyG and BatSynth are now the only two devices that use the (expensive “Tant/Poly”) capacitors with polarity – the “CAP TANT POLY 47UF 10V 1206“. These have two metal contacts at the ends on the bottom, and on the top are usually all black, apart from a grey (or white) band at one end. The PCB will have a white box at one end of the component position, and the grey band goes at this end.

Note: The Griff and mini Griff used to use “tant/poly” capacitors, and the silkscreen printing still shows the polarity for them. However on Phils current Griff component list he does not recommend using the expensive “Tant/Poly” capacitors with polarity and just uses cheaper Ceramic 47UF capacitors instead.

The position of the microphone is critical, as you only have a 0.7mm hole in the PCB for the sounds to pass through, so accuracy is everything.

Fortunately Phil has a outline of the mic printed on the PCB so you should aim to get the microphone in the dead centre of this.

• The gold side of the microphone goes upwards, with the other side with two dots and a ring going next to the PCB on the bottom.
• Look for the two dots and the ring on the PCB, and check that the mic is going the right way around by looking at the mic underside, before you place it.

Phil specifies “bottom firing” LED which have a clear lens bump on one side. This clear bump goes down though the hole in the board.

On the top of the LED there are two metal contacts with a green T shape printed in between. As these are diodes they only work one way, and so the tail (bottom) of the T shape always points towards Ground on the board. This is often to the outside of the board, but check the component layout for your particular device.

The integrated circuits (IC) also can only go one way round (have polarity). These are like ants or insects with metal legs pointing down.

There will be a dimple on the top of the IC, this indicates pin 1, and a corresponding dot or star on the PCB to indicate where this pin1 goes.

It is much easier now as the single channel Op Amp. IC is asymmetric, with three legs on one side, and two on the other, so impossible to fit the wrong way.