I suspect that if bad actors can add circuitry and ask for a small
rogue chip be mounted on a board, that same bad actor can delete the
laser scribe in the area they want to use.

On 10/18/18, Ahmad, Syed <[log in to unmask]> wrote:
> Would it help disable embedded spy chips if we label all empty areas on the
> boards with lasers?
>
> -----Original Message-----
> From: TechNet <[log in to unmask]> On Behalf Of Wayne Showers
> Sent: Tuesday, 16 October, 2018 10:44 AM
> To: [log in to unmask]
> Subject: Re: [TN] Incompatible Labels
>
> I can write a book or at least a pretty good paper on the pros and cons of
> each of laser, label, and inkjet and they all have their issues, but in
> order of best to worst.
>
> Laser onto a white silkscreen marking square, this is the best for
> permanency. Legibility (HRI) is very good.  The barcodes, especially 2-D
> (MRI) can be a little hard to get a good reading on but a good scanner
> helps.
> Best is to have a copper pad, with solder mask and silkscreen over it.
> Issues: can (will) expose copper so, cannot cross traces.
>
> For a label, Brady Hi-Temp with thermal transfer and acrylic adhesive
> backing.  Up to 4 SMT reflows have no impact and actually help label
> adhesion.  They do NOT like wave solder.  The trick to maintaining the
> printing is to actually send the labels through at least one thermal profile
> (apply labels BEFORE SMT).
> * I did a mini-validation for a customer with 4 thermal excursions and 10
> wash cycles and maintained legibility throughout.  I also did not lose any
> labels in the cleaner.
> PCB, .062, 4-layer, 1 oz inners, 1/2 oz outers with .001 inch plating, green
> semi-gloss solder mask.
> Label: Brady B-719 Material
>
> Direct Inkjet.  Good process, but sensitive to (1) gloss and over-cured
> solder mask, (2) PCB cleanliness, (3) proper bake on. (1) Gloss and
> Over-Cured solder mask do not provide enough anchor points for the printing
> and can (will) come off in a cleaner.  (2) PCB cleanliness is critical as
> any dirt, debris or oil will prevent the ink from adhering.  (3) Bake on
> time and temperature is critical to getting a good set on the ink.  The
> 2-part inks are less sensitive to (1), but (2) and (3) still apply and a new
> (4) is in play as depending on application method, these inks tend to smear
> at the edges.
>


-- 
Denny Fritz
Consultant
812 584 2687