DVD-98C Transcript
DVD-98C
Sign Recognition for New Employees
in Electronics Assembly
Below is a copy of the narration for DVD-98C. The contents for
this script were developed by a review group of industry experts and
were based on the best available knowledge at the time of
development. The narration may be helpful for translation and
technical reference.
Copyright © IPC – Association Connecting Electronics Industries. All Rights Reserved.
Opening Song Spoof (Signs)
And the sign said, “Electrostatic protection is required here”
That way our components won’t have nothin’ to fear
So I tested my shoe grounders and my wrist straps too
I pray you’re gonna teach me what else I need to do
Chorus
Sign, sign, everywhere a sign
Shipping and receiving and the surface mount line
Do this, don’t do that, can’t you read the signs
And the sign said, “Hazardous waste storage, so you better keep out”
Know the emergency exits, the evacuation routes
Observe proper lifting precautions – when there’s parts to stock
Pay attention to the yellow barrier tape, and stop watchin’ the clock
(Chorus)
NARRATOR
Whoa! Check out all these signs. We see them on the production floor, in shipping and
receiving, in the stockroom and in areas where we store and use hazardous materials. We even
see signs on the packaging of the components we use to manufacture our electronic assemblies.
Many of these signs fall into two categories – signs that caution and warn us about the possibility
of injuring ourselves; and signs that caution us about protecting the sensitive materials that we
store and use in the production environment. By understanding and paying attention to these
precautionary signs, we will be able to work more safely and create the highest quality products
possible.
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DVD-98C Transcript
Safety Signs
Let’s begin with the most important signs – those that involve our personal protection. A
common sign we see as we enter the production area tells us that safety glasses are required.
That’s because many assembly jobs have potential eye hazards.
For example, clipping component leads can create tiny, flying pieces of metal that can injure our
eyes. Similarly, when we’re soldering, or working around automated assembly equipment, our
eyes are at risk. And especially when we’re pouring chemicals. In many facilities, eye protection
is required in all material processing areas. Safety glasses usually include side shields for
additional protection.
Most assembly jobs also include working with some hazardous materials and chemicals. The
Haz-Mat sign – with its familiar diamond shaped symbol – shows the severity of the four levels
of danger associated with a specific chemical. These include the health hazard; how flammable
the chemical is; the reactivity level of the material; and any specific dangers – such as the
warning not to mix water with a particular chemical.
Every hazardous material also comes with a Material Safety Data Sheet, or MSDS. If your job
requires working with hazardous chemicals, you will receive detailed training to learn the
physical and health hazards of the materials, and how to read the labeling system.
You’ll also be taught about the protective equipment you’ll be required to wear when handling
dangerous materials. There are other signs that warn us about hazardous materials – and we
should take them to heart to prevent injury.
The lead that is in tin-lead solder bars, solder wire and solder paste is a poison. But working with
tin-lead solder isn’t the problem. The problem involves handling the solder wire, solder paste or
soldered boards, then touching something you put in your mouth – such as food, cigarettes, make
up or pencils. That’s because ingestion is the most likely route of entry for this toxic material.
The way to avoid ingesting lead in this way is to always wash your hands before touching any
item that will come in contact with your mouth. It can also be helpful to use gloves when
working with tin-lead solder.
At this point, let’s examine the portable safety signs we occasionally see on the production floor.
These include barrier tape – the yellow caution tape around an area that is temporarily off limits
during repair or clean up of spills; and the lock out / tag out – which disables the energy source to
a piece of equipment.
Speaking of equipment, it’s important to make sure our personal appearance doesn’t put us in
jeopardy when working around automated machinery. For example, unrestrained long hair can
be a safety hazard because it can get tangled and caught in the moving parts inside assembly
equipment. This problem can be solved by keeping hair at shoulder length using ties, pins or a
hairnet.
Loose clothing is also a potential hazard for the same reason. In addition, long earrings,
necklaces and large, loose bracelets can be dangerous around certain types of production
equipment – and may result in injury, electrical shock or burns.
Another safety related sign has to do with proper lifting – especially in the receiving, shipping
and stockroom areas. Let’s examine the correct lifting position for picking up a heavy object.
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DVD-98C Transcript
We need to make sure we bend at the knees – not at the waist – and that we’re close to the load.
Then we tighten our stomach muscles – and with our back straight and our lower back curved
inward – we stand up. Notice that we don’t bend our backs. Our legs do the lifting. Also, be
aware that lifting and twisting at the same time will often result in a back injury.
The last, and perhaps most important, safety sign involves evacuating the area in the event of an
emergency. You will need to know both primary and secondary evacuation routes. If there’s
something you don’t understand about how to exit the building, please ask your supervisor.
ESD Signs
Now let’s take a look at the signs we use to help protect our electronic products and components.
We’ll start with electrostatic discharge, or ESD. As we approach the entrance to any production
area, we’ll likely be faced with this sign – ATTENTION – ELECTROSTATIC SENSITIVE
AREA – DO NOT ENTER WITHOUT PROPOER ELECTROSTATIC EQUIPMENT.
ESD is the sudden transfer or discharge of electricity from one object into another. Everybody
knows what it’s like to walk across a carpet, touch a metal doorknob – and feel that zap. That’s
an example of electrostatic discharge.
2000 volts is the lowest level of ESD that most people can feel, but static zaps under 20 volts are
capable of damaging and destroying many of the sensitive electronic components we’ll be
handling every day.
One way to remedy this problem is to drain off the charges that we generate or hold while doing
our jobs in an ESD safe area. The idea is to drain off charges in a controlled manner before they
reach an ESD sensitive item. That’s why the sign says: “Do Not Enter Without Proper
Electrostatic Equipment.”
This equipment typically includes two shoe grounders, or heel straps for standing operations –
and a wrist strap for seated activities. It’s very important to follow your company’s policy for
testing heel and wrist straps at regular intervals. Wearing defective personal grounding
equipment will cause ESD problems – and we won’t even know it.
If we’re lucky, the circuit board assembly will fail electrical test – and the component can be
replaced. The biggest problem occurs when the component is weakened and passes electrical
test. The circuit board assembly is then installed in the final product – and the product is sold.
At some point the ESD damage causes the component to fail – resulting in an unhappy and
frustrated customer.
Here’s how one ESD tester verifies that our personal grounding equipment is functioning
properly. Notice that with heel straps, we’ll need to test each foot separately. That’s because
testing both feet at the same time will not cause a failure in one strap unless both straps fail.
When testing wrist straps, it’s important to shake our wrists to check for intermittent failures.
ESD sensitive components are stored in static shielding packaging that will have ESD caution
labels that read: ATTENTION – STATIC SENSITIVE DEVICES. That tells us that we may
only remove the components from the packaging at ESD safe workstations; that we must handle
the components using proper precautions; and that we need to keep static generating materials
away from these devices.
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DVD-98C Transcript
ESD sensitive components should only be handled at an ESD safe workstation – consisting of a
grounded static dissipative work surface and static dissipative flooring. These dissipative
materials are partially conductive – meaning they are conductors of electricity – but they do it
slowly enough to leave ESD sensitive devices undamaged.
Improper handling of ESD sensitive items – even when we’re properly grounded at an ESD safe
workstation – can cause damage to components and assemblies. For example, sliding a
component across a work surface generates static charges and can injure the component. It’s best
to pick up the component, move it, and then set it down. It’s important to handle the body of the
component, rather than the leads. The leads are the most conductive pathway for an ESD zap.
In terms of circuit board assemblies, they should be handled only by the edges – minimizing
contact with any conductive surface. Because all the components are connected, ESD damage to
one component can spread to others.
Static generating materials are also a problem for ESD sensitive devices. For example, many
common office materials might appear harmless, but when brought into an ESD safe area, they
can cause an event. Many of these materials generate and hold static charges. Examples include
common plastics; styrofoam food and beverage containers; vinyl binders; and post-it notes and
other paper products.
The best remedy for this problem is to remove as many of these non-conductive items from the
workstation as possible. When a static generating material is necessary for our job, there are
several methods available for reducing the effect of these items.
These include applying an anti-static solution to hand tools at regular intervals; using air ionizers
to neutralize charges that accumulate on non-conductive items; and to operate with controlled
humidity – since dry air tends to make ESD problems worse.
MSD Signs
Another type of component that requires protection is the moisture sensitive device, or MSD.
There are a variety of precautionary symbols and labels on MSD packaging.
An MSD is an electronic component that is encapsulated with plastic compounds and other
organic materials. These materials allow moisture from atmospheric humidity to enter that
permeable packaging. An imperfect seal between the integrated circuit die and the package that
surrounds it puts many plastic surface mount packages at risk.
When these types of packages are exposed to a typical factory environment with at least 30%
humidity, moisture can accumulate inside the package. Moisture accumulation is a problem
because the vapor pressure of the moisture inside the package greatly increases when the device
is exposed to reflow soldering temperatures. The exposure to high temperatures can result in the
package cracking -- or the delamination of internal interfaces within the package. Examples of
internal interfaces include the integrated circuit die, bonding wires and ball or stitch bonds.
The proper handling of MSDs goes a long way in protecting these components. There are two
industry standards that deal with the classification and use of MSDs. Becoming aware of
moisture sensitivity levels and baking requirements are especially important.
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DVD-98C Transcript
When possible, MSDs should be kept in their original packaging until used. This packaging
consists of a sealed moisture barrier bag that restricts the transmission of water vapor; a moisture
sensitive caution label that specifies information such as classification level, shelf life, peak
temperature, floor life, baking needs and bag seal date; active desiccant, which is a moisture
absorbent material; and a humidity indicator card that changes color when the specified relative
humidity values are exceeded inside the moisture barrier bag.
There are situations during incoming inspection where we may be required to open the packaging
to verify component part numbers and quantity. When this is the case, it’s best to open the bag
near the top so it can be easily resealed. Before resealing, it’s important to return the desiccant
and humidity indicator card to the moisture barrier bag.
When MSDs are stored in the stockroom, we’ll need to store them so that the older devices can be
removed and used before the newer components. This system of storage is called first in – first
out, or FIFO. FIFO ensures that the older components are put into production before the newer
ones – to minimize the amount of time that the components are held in storage.
Kitting MSDs for use on the production floor also requires some precaution. For example,
expiration dates should be checked on the packaging. It’s also important to verify that the
humidity indicator card has not exceeded 10% relative humidity. If the card has exceeded 10%,
the devices will need to go through a baking operation to remove the accumulated moisture
before being soldered onto a circuit board assembly.
Floor life is also an issue for MSDs. If the exposure to the factory environment exceeds a
specified time, then the MSDs will need to go through a baking operation – often 48 hours long –
before they can be safely reflow soldered, or be returned to the stockroom for storage.
Lead Free Signs
Now, let’s take a look at the signs related to lead free soldering. There are a variety of signs and
symbols that designate lead free processing areas, solder alloys, components and circuit boards.
Until recently, the majority of solder connections were made with tin-lead solder.
Our industry has been transitioning from tin-lead to lead free solder alloys. The lead free alloys
offer potential benefits for both personal safety and for the environment. Here are some things to
be aware of when working with lead free solder.
Tin-lead solder melts at 183 degrees centigrade. The lead free solder alloys require a higher
temperature to become liquid – often 40 degrees C higher than tin-lead. The higher temperatures
represent the most significant difference between the tin-lead and lead free processes. And these
higher temperatures do present a number of challenges.
For starters, components and circuit boards need to be able to withstand the increased heat.
That’s because the lead free alloys tend to have a higher surface tension – meaning they won’t
spread along the surface of the connection as easily as their tin-lead counterparts. This often
results in increased dwell times, or the time that the soldering iron is in contact with the
connection – compounding the heat problem. Another temperature issue relates to MSDs. These
components will need to be handled with even greater care in a lead free process.
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DVD-98C Transcript
Lead free solder connections tend to have a different visual appearance than tin-lead solder joints.
As you can see, the lead free connections appear a little grainier than their tin-lead counterparts.
Let’s examine a sampling of target solder joints – comparing lead free to tin-lead – for both
plated through-hole and surface mount connections.
An important issue for companies that use both lead free and tin-lead solders is cross
contamination. Cross contamination occurs when different solder alloys are mixed – specifically
tin-lead and lead free solders. Cross contamination may create unreliable solder connections.
There have been studies that show that certain lead free and tin-lead mixed solder joints develop
cracks and other types of physical instabilities. There is also evidence that cross contamination
can even become a reliability issue when different lead free alloys are mixed.
But the biggest problem with mixing tin-lead and lead free solders is that it will make our
electronic assemblies and electronic products non-compliant with European Union standards.
Companies that are found non-compliant will not have their products accepted. That means they
can’t be sold. As you can imagine, this situation would be financially crippling.
Summary
You’ve just been introduced to many of the important signs you’ll come across in electronics
assembly. We’ve examined the signs that alert us to personal safety issues; to ESD prevention
and control issues; to MSD prevention and control issues; and to lead free soldering concerns. By
recognizing and paying attention to the signs we see, we will be able to work more safely and
create the most reliable high quality products.
Signs Spoof (cont’d)
Sign, sign, everywhere a sign
Shipping and receiving and the surface mount line
Do this, don’t do that, can’t you read the sign?
And the sign said, “Safety glasses should be on your head”
Put that respirator on, and no eating bread
From moisture sensitive devices to the lead free line
Spontaneous chemical reactions, danger: flammable signs
(Chorus)
v.2
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