Franklin,

I believe you may misunderstood my problem.

The solder in the via holes is actually residues from the HASL process. So,
during the IR reflow, it came out (via holes facing downward) & form solder
lump at the annular ring of the via holes. It's not total disaster but a
pain in the ass for assembly house.

As I see it, most of the affected via holes are those below 22 mil (hole
size). Is there any limitation for the air knife to totally clear off the
excessive solder?

My understanding from one of our customer's spec did indeed specify that
solder in via holes <22mil is allowed. Other than this spec, what's the
common practice by PCB maker or user.

Appreciate all your inputs.

Regards,

Jacob Pao

-----Original Message-----
From: Franklin D Asbell [mailto:[log in to unmask]]
Sent: Wednesday, September 27, 2000 8:14 PM
To: TechNet E-Mail Forum.; Pao, JacobKH
Subject: Re: [TN] Solder in via holes after HASL process


Jacob,

Actually IPC 6012 states the opposite, vias may be completely plugged.
If you have access to 6012 look at table 1-1 for plated holes (including
vias).

When plating is not desired in vias the requirement is typically to tent
them with solder mask.

Franklin


"" wrote:

>
>
> Technetter,
>
> 1) Is there any spec that says no solder is allowed in via holes
> (<22mil) especially the HASL boards?
>
> I've encountered a numerous of HASL boards with this problem. Due to
> the solder in via hole, solder lump will start to form at the annular
> ring of the via holes & it causes uneveness solder paste printing as
> well as posibilities of damaging the solder paste stencil. The solder
> lump will only form after the first IR reflow & with the via hole
> facing downward. When it's going for its second round of SMT, the
> problem start to appear, bridging.
>
> 2) Is there any recommended solutions to this problem?
>
> Another input, most of these boards were plugged either from the
> primary or the secondary side. In my case, we'll always mount the
> plugged side first & then followed by the other side.
>
> 3) Is there such a design rule that the process has to go the other
> way round? Meaning, mount on the unplugged side first insteads of the
> plugged side.
>
> Regards,
>
> Jacob Pao (SQE)
>